Jeff Mathis has started 836 regular-season games behind the plate, ninth-most among active catchers. He has played in the majors for 16 years and made more than $20 million. And, oh yeah, he turns 38 at the end of the month.

Why then, after all that, would he want to sign a minor-league deal and fight long odds to compete for a job in spring training?

“Because,” Mathis said by phone this week from the Phillies’ camp in Clearwater, Fla., “it’s all I know.”

Indeed, Mathis has spent half his life in professional baseball. He got drafted out of a Florida high school at age 18 and promoted to the big leagues at 22. Four years after that, in 2009, he called the final pitch of the last playoff series won by the Los Angeles Angels. He has since played for the Toronto Blue Jays, Miami Marlins, Arizona Diamondbacks, and Texas Rangers, the latter two teams awarding him two-year contracts.

Mathis is the very model of a modern backup catcher — or, as Phillies star J.T. Realmuto puts it, “the exact person you want for that role.” And it’s a testament to his defense, game-calling, and ability to relate to pitchers that he has been in demand for so many years despite batting .194 with a .553 OPS in 3,006 career plate appearances.

So, when the phone didn’t ring with a major-league offer this winter, Mathis had a choice: Take what he could get to keep playing, or retire. He picked Door No. 1, even though it meant six weeks of 8 a.m. blocking drills on backfields with catchers who are 15 years his junior.

“I just wasn’t ready to shut it down,” Mathis said. “I wasn’t ready to sit on the couch. There weren’t a whole lot of options out there. Had this opportunity on the table and just figured I’d take advantage of it, meet some more people, give it another go, and see what happens.”

Some things have happened. Realmuto fractured his right thumb while blocking a pitch in the dirt a few days before spring training began. Then, last week, prospect Rafael Marchan — one of three catchers on the Phillies’ 40-man roster, with Realmuto and Andrew Knapp — strained a hamstring and will be out until almost the end of camp.

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Is it enough to put Mathis in the running for an opening-day roster spot? Probably not, especially once Realmuto was cleared Thursday to remove the splint that replaced his cast last week and ramp up his throwing, hitting, and other baseball activity.

But just as the upstart prospect who plays himself into contention for a roster spot is an annual spring-training narrative, the veteran trying to hang on is equally compelling theater. As long as there’s a chance, Mathis will keep showing up. He might even pop an occasional home run, as he did Wednesday against Detroit Tigers left-hander Matthew Boyd.

“I’ve been happy with the way my body’s felt because that was something I was a little worried about,” Mathis said. “But to be out there and moving around, I’ve already played up to six innings and came out OK. I definitely can’t complain in that regard.”

The Phillies are pleased to have Mathis, too, as a mentor to their catching prospects. He works out in the same group as 23-year-old Rodolfo Duran and 21-year-old Logan O’Hoppe, offering tips and sharing observations.

His scouting report: Watch for O’Hoppe.

“We were taking BP the other day and he was hitting some balls as far as I’ve seen people hit it in a while,” Mathis said. “He’s a big, strong kid but is able to move around, too.”

It isn’t only the young catchers who have benefited from Mathis’ presence.

Realmuto, his teammate in Miami before becoming a two-time All-Star, likes to “pick his brain as much as I can.” Mathis has also gained a reputation as something of a “pitcher whisperer.” Spencer Howard smiled slyly about a “stellar mound visit” that Mathis made earlier this week and called him “an overall great dude.”

“He’s done a great job his whole career at working with pitchers and being good behind the plate, not to mention he’s an unbelievable teammate,” Realmuto said. “What he does off the field, you can’t really quantify or calculate.”

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For the first half of his career, Mathis was a favorite of then-Angels manager Mike Scioscia, the former catcher from Delaware County who insisted on high-quality defense behind the plate. Phillies manager Joe Girardi describes Mathis as a smart player who did what was needed to stay in the lineup despite his meager offense.

Mathis can imagine coaching when his playing career finally ends, another reason he wanted to spend spring training with the Phillies. Girardi caught for 15 years in the majors before transitioning to coaching and eventually managing. It’s a path that Mathis could take, sooner than later.

“Being able to be around Girardi, with the track record that he has, seeing how he goes about it day in and day out is something that I was excited about,” Mathis said. “It’s been pretty cool. I’m glad I’ve been able to see it.”

Mathis said his contract includes a March 24 opt-out clause. If he exercises it, the Phillies would have 48 hours to place him on the 40-man roster or grant him his release.

Could they talk him into staying on as a member of their taxi squad, enabling him to travel with the team and serve as a bullpen catcher at home but not requiring that he be added to the 40-man roster unless he’s activated to play? Maybe, but he also has two young daughters at home.

“It’s something that I’ve thought about a little bit, but I’ll explore more when we get there,” Mathis said of his future in the game. “Talk to the family and see what’s out there maybe elsewhere and just kind of go from there.”

Wherever it takes Mathis, this spring has given him the chance to keep putting on the catching gear.

And that’s all he really wanted.

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