Phelps limited the Orioles to one hit with six strikeouts in four scoreless innings on Saturday in a 5-3 loss, pitching in relief of Phil Hughes and showcasing what he said was his best curveball of the year.
Phelps also pitched effectively last year as both a starter and a reliever, and manager Joe Girardi believes that Phelps has made the necessary adjustments to be successful in either role.
"He'd been a starter his whole career, but it was basically the way we used him last year, so I think he has an understanding of how to prepare, what he needs to do to get going," Girardi said.
"He did a tremendous job [on Saturday]. You can't ask a guy to do a better job. It's a role that he has had to learn, and I think he has adjusted pretty well."
Phelps said that to warm up as a starter, he usually throws 35 pitches, but in his relief role, he can be ready with as few as 15. Although he has said that he ultimately would like to be a starter, he's happy with his current assignment.
"I'm not out here hoping our starters don't do well," he said. "I want to win games regardless of what my role is. I'm pulling for those guys as hard as they're pulling for me.
"I have faith in them; we've all had rough outings. Our guys usually have more good ones than bad ones. I'll just go out and do my job and let it take care of itself."
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.