NEW YORK — To give their starters an extra day of rest amid a stretch of 16 games in 16 days, the Phillies recalled left-handed pitcher Bailey Falter from triple-A Lehigh Valley on Friday to start that night’s game in New York against the Mets.

The Phillies optioned veteran left-handed reliever José Alvarado to triple-A Lehigh Valley as a corresponding move. It was a somewhat surprising decision, given that it leaves manager Joe Girardi with only one left-handed reliever in his bullpen in Brad Hand, but Alvarado has been struggling this season.

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As of Friday, the left-handed reliever has a 7.62 ERA over 13 innings pitched. Over his last seven games he has a 13.50 ERA in 5⅓ innings pitched. What concerned Girardi, above all else, was Alvarado’s inability to get left-handers out. Last season, lefties hit just .123 against him. This season, they are batting .333.

“I just think his sinker is not sinking the way it is, and we just have to get him back on track,” Girardi said Friday. “And it’s hard to get people work at this level to get them back on track. So hopefully this is just time out to get him where he was, and he’ll be dominant for us again.”

The Phillies’ bullpen currently sits at No. 22 out of MLB’s 30 teams in ERA at 4.21. They have the second-most walks in baseball with 85, a problem Alvarado, with his 15.4% walk rate, contributed to. But despite these unsatisfactory numbers, Girardi said the choice to move Alvarado to triple A was not meant to send a message to the bullpen or the roster as a whole.

“What we’re trying to do is we’re trying to get him to where he’s an extremely valuable piece again,” he said. “That’s the most important news.

“I think (Alvarado) understands what we’re trying to do and how much we care for him. There have been other guys who have went through this. Héctor (Neris) went through this and came up and was pitcher of the month. (Jeurys) Familia went through this a couple of years ago, and he came back and has been really successful. So this is for the long term. We want to get him back on track.”

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Girardi said that as of now, there are no plans to move Falter back to the bullpen, so Hand will remain the Phillies’ only lefty reliever for the foreseeable future.

Mickey Moniak update

Mickey Moniak has not been wasting any time in hitting his offensive stride as he continues his rehab assignment. Through six games between single-A Clearwater and double-A Reading, he’s hit .375/.429/.625. The Phillies were contemplating calling Moniak up to join the team in New York, but Girardi said Friday that it’s unlikely the center fielder will be called up this weekend.

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“He’s off today because he’s played a bunch of days in a row,” Girardi said. “He’ll probably play the next couple and we’ll re-evaluate. Right now, we have not had discussions about calling him up this weekend.”

Didi Gregorius feeling better

Shortstop Didi Gregorius, who was placed on the injured list on May 7 (retroactive to May 5) with a left knee sprain, said he has been able to do just about everything on a ballfield but hit with cleats on the dirt. The poor weather hasn’t helped with that; Girardi was hoping to get Gregorius on the field Friday, but he wasn’t able to because it rained before the Phillies game in New York.

Regardless, Gregorius said he feels better. He expects to have a better timeline for when he’ll return to the big league club by Saturday. Girardi said when Gregorius is ready, he’ll be sent out on a rehab assignment.