"I felt good, my arm felt good, but it was frustrating," said Phelps, who ended up on the ground in the fifth inning when Justin Upton slammed an RBI single up the middle, then served up a two-run homer to Juan Francisco.
"I just didn't bear down [in the fifth inning] after I got two outs," said Phelps, who is 2-2 with 12 strikeouts and four walks in five starts. "I gave up that walk [to Jason Heyward], and then it snowballed. Anytime I end up on my back, it's never good. This was probably the best I've thrown, command-wise and stuff-wise, all spring."
"Before that inning, I thought he threw the ball very well," said manager Joe Girardi. "This was a progressive game for him. I'm OK with that. This young man knows how to pitch."
Phelps is locked in a battle with Ivan Nova for the fifth spot in the rotation, assuming injury-prone Phil Hughes is able to open the season as the fourth starter.
So far, Phelps and Nova have both pitched well enough to demonstrate they belong. And, depending upon how Hughes progresses, they could both begin the season in the starting rotation. In that case, Girardi has said, the competition between Phelps and Nova "could become a moot point."
"Both have got to continue to pitch," Girardi said. "I feel good about our rotation. I feel good about our staff."
Nova, who is scheduled to start Sunday against the Pirates, is 0-0 with a 1.00 ERA, five strikeouts, one walk and no home runs allowed after three appearances this spring.
And Phelps isn't taking anything for granted.
"I don't feel I've achieved anything to this point," he said. "We've still got 12 days of camp left. I'll let you know when they announce the roster."
Phelps, who made his Major League debut in 2012, pitched in long relief last season, while Nova, plagued by shoulder problems, saw his performance plummet in the second half.
Nova has the edge in experience and is the harder thrower. But Phelps has shown he could serve as a swingman.