Free-agent quarterback Brock Osweiler says he is retiring from the NFL.

The former Denver Broncos, Houston Texans and Miami Dolphins quarterback told 9News in Denver in a telephone interview that he was "extremely grateful for the time I did receive playing in the National Football League."

"The experiences I did have, people I did meet, relationships I did make -- I'm not going to dwell on the things that didn't happen in my career.

"Being a kid from Kalispell, Montana, playing for the Denver Broncos, winning a Super Bowl, having the opportunity to sign a second contract -- when you look back on it, I couldn't be more appreciative. It was great."

Osweiler, who is 28, went 2-3 as a fill-in starter for the Dolphins last season when Ryan Tannehill was injured. He gave the fan base hope in a period dubbed "Brocktober," which began with him throwing for a career-high 380 yards in an upset overtime victory against the Chicago Bears, but his play leveled off in the following games.

What Osweiler did do, however, is reestablish his career from disappointing starter to reliable backup quarterback. He signed a one-year, $880,000 contract with Miami and competed to make the roster as a backup. Despite a rough training camp, the Dolphins kept Osweiler as their No. 2 QB, and he kept them afloat when Tannehill got hurt early in the season.

In 2018, Osweiler completed 63.5 percent of his passes for 1,247 yards, 6 touchdowns and 4 interceptions.

Osweiler's biggest NFL contribution came in a similar role. He went 5-2 as a starter in place of an injured Peyton Manning for the 2015 Denver Broncos, helping them earn the AFC's top seed en route to a victory in Super Bowl 50.

"That 2015 season is something that is very special,'' Osweiler told 9News. "The coaches, the players, they mean the world to me. I was thankful to have had the opportunity to play the role I did, but that was the ultimate team deal. There was a ton of talent on that football team, but I would say we were the closest of all teams in the National Football league. Our culture was beyond anything that can ever be created. It was so genuine, so real that I think any coach or player on that team would have done anything for anybody in that building that year."

That season led to a $72 million contract with the Texans, who traded him to the Cleveland Browns after one difficult season as the Texans' starter. The Browns then released Osweiler just before the 2017 season, when he was again picked up by the Broncos.

Osweiler, who played seven seasons in the NFL, was drafted by the Broncos in the second round (57th overall) of the 2012 draft.

"I have my health. I have the ring. There's a lot of things I still wanted to accomplish. And I have a lot more left in the tank. But, hey, sometimes you don't get that opportunity. And given that, it's all good," he told 9News.

ESPN's Cameron Wolfe contributed to this report.