Nick Castellanos says the Phillies’ outfield rotation is ‘a big adjustment.’ Rob Thomson gets his frustrations.

Nick Castellanos poked his head into Rob Thomson’s office before a recent series to ask about the manager’s plan for splitting playing time among the Phillies’ five outfielders.

It isn’t a familiar situation for him.

Over the last 10 full seasons, Castellanos averaged 146 starts. Last year, he became the first Phillies player to start all 162 games since Jimmy Rollins in his MVP 2007 season. Since 2014, no outfielder has played more games than Castellanos.

Lately, though, with Castellanos in the midst of a season in which he has produced at a below-league-average rate, the Phillies are using him as one-fifth of an outfield rotation. Since Aug. 9, he has started 16 of 21 games, sitting out one game in five of seven series.

» READ MORE: Andrew Painter has taken his lumps in triple-A. Adding him to the Phillies’ roster in September could still bring benefits.

“It’s a big adjustment,” Castellanos said Friday night.

To make it easier, Thomson said he tries to give Castellanos — as well as Brandon Marsh, Max Kepler, Harrison Bader, and Weston Wilson — advance notice of when they will be in the lineup. But Marsh, for instance, is more accustomed to playing against righties and sitting against lefties.

How has Castellanos dealt with not knowing for sure that he will be in the lineup every day?

“The best I can,” he said.

Thomson insisted Saturday that the Phillies don’t have a simmering issue with Castellanos.

“Nick just wants to play, and that’s it,” he said. “I think most guys get frustrated when they don’t play. Because they want to play, and that’s normal.”

But Castellanos also expressed frustration Friday night after being replaced for defense in the ninth inning of a 2-1 victory. It marked the first time since June 16 in Miami that Thomson substituted for Castellanos. In that instance, Castellanos made what Thomson called an “inappropriate” comment and got benched.

This time, because Castellanos was on base in the eighth inning, first-base coach Paco Figueroa informed him that he was coming out of the game while Thomson brought the lineup card to home-plate umpire Alfonso Márquez to communicate the changes.

» READ MORE: Kyle Schwarber — and his four homers — kept the Phillies centered after a rough week. He always does.

Thomson said he saw Castellanos before Saturday’s game but didn’t speak with him about taking him out for defense. Castellanos entered the weekend ranked last among 113 qualified outfielders in outs above average (-12) and third-worst in defensive runs saved (-13).

Castellanos also was batting .253 with 16 homers and 61 RBIs. Among 152 players with enough at-bats to qualify for the batting title, Castellanos ranked 139th in on-base percentage (.294), tied for 103rd in slugging (.406), and tied for 134th in OPS+ (89, or 11% below league average).

Kepler, an everyday outfielder for most of his career before signing with the Phillies, was irritated earlier in the season over splitting time in left field. But “at this point I’ve accepted it,” he said recently, adding that “we want to win ballgames, and I’m going to do whatever I have to do.“

“I think we’re all at the point now where we’re all-in,” Thomson said. “Whatever is best for the team to win a game that night, we’re all-in. Check your ego at the door and let’s go.”

Is Castellanos capable of that?

“Oh, absolutely,” Thomson said. “Hey, look, we don’t need to make a big deal out of this. He’s frustrated because he wants to play, and that’s it. I understand that. I wouldn’t respect a guy if he wanted to come out.”

Maybe Castellanos will fall in line. Or maybe he will heat up at the plate, which would lead Thomson to revert to writing his name in the lineup every day.

» READ MORE: Inside Rob Thomson’s process to ‘mix and match’ playing time among the Phillies’ five outfielders

Team officials have met throughout the weekend to discuss the expanded September rosters. Beginning Monday, teams are allowed to carry 28 players instead of 26, including a maximum of 14 pitchers.

The Phillies are expected to bring up one pitcher and one position player.

It’s possible the Phillies could recall utilityman Otto Kemp, who was 13-for-40 (.325) with four doubles, one homer, and eight RBIs through 10 games after returning to triple-A Lehigh Valley a few weeks ago.

Johan Rojas, 26-for-84 (.310) in 19 games since getting sent to triple A, is also a candidate for a return to the majors. But trade-deadline addition Harrison Bader has played well in center field. Rojas may benefit from staying in triple A.

The Phillies could also consider bringing back popular catcher Garrett Stubbs to provide depth behind the plate with J.T. Realmuto and Rafael Marchán.

Top prospect Andrew Painter is lined up to start Wednesday for Lehigh Valley. Painter has a 5.36 ERA in 19 triple-A starts. ... Jesùs Luzardo (12-6, 4.23 ERA) is scheduled to start at 7:10 p.m. Sunday against Braves righty Hurston Waldrep (4-0, 0.90).