SAN FRANCISCO -- The Phillies could not continue with Bailey Falter in the rotation, so Tuesday they optioned him to Triple-A Lehigh Valley.

“It’s just a reset,” Phillies manager Rob Thomson said. “Go down there, get outs, get some confidence, you know? It’s really what it’s all about.”

It seemed clear that the Phillies needed to do something with Falter, who fell to 0-7 with a 5.13 ERA following Monday’s 6-3 loss to the Giants. What is far less obvious, however, is how they replace him. The Phillies have no clear answer because the organization finds itself in a serious crunch for starting pitching.

“I don’t know if you can ever have too much starting pitching depth, but we’ve been tested here in the early going,” Phillies general manager Sam Fuld said. “We still have confidence in Bailey, and we still have confidence that we have some guys who can step up. But there’s no doubt that we can benefit from a deeper bench when it comes to the starting rotation.”

The Phillies need a starter for Sunday’s series finale against the Cubs at Citizens Bank Park. They could have pitched Zack Wheeler and Taijuan Walker on normal rest Sunday and Monday, respectively, pushing back the Phillies’ No. 5 spot until Tuesday, but the Phillies prefer to give Wheeler and Walker the extra rest.

Thomson said they might use the bullpen Sunday if it is fresh. If not, Thomson said they would turn to a pitcher not on the 40-man roster.

Triple-A right-hander Noah Skirrow is the most likely candidate.

Skirrow was 4-0 with a 3.52 ERA in six games (five starts) with the IronPigs before he allowed five runs in 3 2/3 innings Tuesday against Worcester.

“It’s been really encouraging to see how he continues to develop,” Fuld said. “He’s always been a guy who throws strikes and competes. He can land multiple secondary [pitches] for strikes. It’s a good slider. It’s a changeup that has continued to develop well. More than anything, I think he’s just not afraid to pitch to contact and challenge guys. He’s continued to trend in the right direction.”

“Strike thrower,” Thomson said. “The stuff is not going to overwhelm you, but he throws strikes and he knows how to pitch.”

“And he’s Canadian,” Thomson joked.

The only healthy options on the 40-man roster are Triple-A left-handers Cristopher Sánchez (0-2, 6.14 ERA) and Michael Plassmeyer (1-3, 6.19), but neither has pitched well, which is why the Phillies are looking for help outside the 40-man. IronPigs right-hander Nick Nelson (1.25 ERA in 21 2/3 innings in three levels) is on the seven-day injured list with an injured left glute. Previously, Thomson said he sees Nelson as a multiple-inning reliever rather than a starter, although perhaps that thinking changes whenever Nelson returns.

The Phillies’ top three pitching prospects are not options. Top prospect Andrew Painter is still recovering from a UCL injury. The Phillies hope he is pitching competitively this summer. No. 2 prospect Mick Abel is 2-2 with a 5.40 ERA in six starts with Double-A Reading. He allowed nine runs in 3 2/3 innings in his last start. He needs to throw strikes more consistently before he becomes a serious candidate. No. 3 prospect Griff McGarry has made only two starts since returning from the injured list. He is just beginning to build up as a starter.