Roman Harper picked up the phone on a sweltering 2006 summer day and called home.

The rookie’s first NFL training camp had just started and he wasn’t sure how he was going to make it through.

“I don’t know if I want to do this anymore,” the New Orleans defensive back told his dad, listening on the other end of the line.

“Just look at that check they just cut you,” the newly minted second-round pick’s father responded.

Fair enough. But Harper, a central part of first-time head coach Sean Payton’s inaugural draft class, was just learning what he and the other Saints were in for.

“We were in Jackson, Mississippi, it was hot every day, it didn’t rain, there was no days off,” Harper told The Post recently. “We were practicing at Millsaps College, where the facilities weren’t great. The turf field was like 114 degrees. It was melting cleats. We had to go uphill like 100 yards to another practice field or 150-200 yards to get to the down field. For rookies it was like a mile walk, the inconvenience of everything, it was awful.

“So you have all of that on top of being a rookie, trying to figure everything out, getting yelled at, getting blamed for everything. At that point you don’t realize that the coaches coach the other players through yelling at rookies. It’s the mental strain, you’re no longer the star, you’re trying to figure everything out. …

“After that year, every other year was cake. Especially when that’s all you know.”

That particular year featured extenuating circumstances. In the continuing aftermath of Hurricane Katrina a summer earlier, New Orleans spent multiple extra weeks at Millsaps while rebuilding efforts continued in their city. Not only that, but Payton was taking over a team he planned to entirely overhaul, so he put it to the test.

The weeks were so rugged, defensive assistant Joe Vitt — now reunited with Payton in Denver — referred to the 2006 Saints as the “Junction Boys” in a nod to the infamous 1954 Bear Bryant Texas A&M team that suffered through its grueling preseason camp and a high attrition rate.

“As we got older and all became wily vets, he would tell stories about the Junction Boys, that’s what they called the group of us that was there that very first training camp and made it through and then continued to have careers later,” Harper said. “He’d always say, ‘We probably took years off their careers.’ I’m like, Joe, that’s not something to brag on, bro. I played 11, but it was tough.

“He was like, ‘You probably would have played 13 if you weren’t one of the Junction Boys.’”

Payton’s first camp with the Broncos will not be quite like that. For one, the NFL has changed its camp rules over the past 17 years. Two-a-days have been outlawed since 2011, and the 2020 collective bargaining agreement further tightened practice rules.

Harper also thinks this particular Broncos team is more established than New Orleans was then.

However, those who have been through a Payton training camp previously expect the Broncos to have a much different experience than a year ago under first-time head coach Nathaniel Hackett.

“We went like a full month of two-a-days,” former New Orleans linebacker Scott Shanle told The Post. “Scott Fujita used to joke that we should make shirts that said, ‘On the 30th day they rested.’ They were brutal, now.

“But Sean was going to try to break you down and find out what you’ve got in a team. The way he’ll do that now is maybe not with all the padded practices, but the days are going to be long, they’re going to be intense.”

Back to football basics 

A year ago, the buzz around Hackett’s first training camp featured regeneration days — lighter workloads every third practice or so — and a near-total absence of one-on-ones and seven-on-seven work and live tackling.

The goal, Hackett and his staff said, was to keep the team healthy and get as many full-team reps as possible. Virtually none of the Broncos starters played in the preseason.

The approach did not work in terms of keeping the Broncos healthy, certainly, and ultimately the entire thing is judged as a failure considering Hackett’s 4-11 mark before becoming the first coach in franchise history to be fired during his first season.

Payton in March called the previous regime’s setup “much, much different than what I’m used to.”

It’s clear his camp is not going to feel the same.

“I do know that we’re playing tackle football and you have to practice tackle football,” he added during the NFL’s spring ownership meeting.

Most or all starters will get reps during the trio of preseason games. “Absolutely. That’s the pre-season,” Payton said.

“This is my 14th training camp, so I don’t think he can throw anything at me that I haven’t seen,” veteran safety Kareem Jackson said earlier this month. “I’m looking forward to it. I’m excited. He’s kind of been telling everybody it’s going to be different, it’s going to be a change, so I’m looking forward to it and embracing it.

“For us as a team, I think it’ll be great for us. I think we need it, to have that culture shock and to see something different and to see how a different ship is ran.”

Another point of emphasis for Payton: Situational football. During the offseason program, he said he and the Broncos were working their way through 43 unique end-of-game situations, a process that will continue in camp.

“It’s no shot at any coach I’ve had, but you can just tell he’s been as successful as he has because of the way he’s come in and how detail-oriented he is,” veteran safety Justin Simmons said earlier this month. “He’s been great. I’m just really excited. The best way I can say it, for me, is how educational it is.

“He competes. That’s the thing I like the most.”

The “aircraft carrier”

Fujita, the veteran linebacker with the 2006 T-shirt idea, decided enough was enough during that “Junction Boys” training camp.

Harper recalled him instructing the Saints one day to hit the practice field sans pads.

You can guess what happened next.

“We got yelled at and cursed out and we had to go put on pads,” Harper said. “We got smacked down like our parents told us ‘Get back in that room and put them clothes back on.’”

Harper, looking back, calls the experience “bananas” but said it played a major role in why that group took the league by surprise, started 5-1 and won the NFC South with a 10-6 mark. Harper started the first five games that fall before an injury ended his season. He started 108 total in New Orleans (124 games played) while playing nine of his 11 seasons for Payton.

Now the coach’s first training camp with the Broncos is at hand. Last month, Payton likened it to, “getting on an aircraft carrier for six months here. You’re here seven days a week well past midnight.”

Former Saints expect a somewhat modified approach that aims at reaching the same goal accomplished in 2006.

“You want to take the first bus out of Denver? Go out and bust plays in a walk-through and don’t take it seriously,” Shanle said. “You will be focused at all times, no matter what the pace and no matter what the padded practice schedule is. So I would say the attention to detail will still be like what it was when we were going two-a-days every day at Millsaps in Jackson.”

Added Harper: “(Payton’s) going to continue to push guys’ buttons, continue to test guys mentally and continue to sharpen the knife of everybody. The mental pressure is just as breaking as the physical pressure, and for most people, the mind will break long before the body ever breaks down.”

That sounds good, actually, to Jackson.

“Going into training camp, you’re kind of seeing what you have as a team and, on paper, you know, I feel like we have a pretty complete roster. Both sides of the ball,” Jackson said. “So each and every year you try to go out and take advantage of the opportunities.

“For us, it’s all about coming into training camp and working toward that first game and putting everything together so everybody can be a piece of the puzzle to help us win.”

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