Phelps permitted a single to Red Sox third baseman Will Middlebrooks in his scoreless two innings of work during New York's 8-6 loss to Boston, but that has been the only blemish the 25-year-old has incurred in 7 1/3 scoreless innings since his July 18 recall.
"I think that consistent work has helped him as much as anything; the innings he was able to go down and get built back up and got his arm strength going again," Yankees manager Joe Girardi said.
Phelps is in his third stint with the Yankees this year and has made 16 relief appearances, striking out three batters in the eighth inning on Saturday. On Wednesday in Seattle, Phelps threw 1 1/3 perfect innings for his second Major League win, and on July 22 in Oakland, he retired all five Athletics he faced, with three strikeouts.
Phelps also made three starts for the Yankees this season and is 2-3 with a 2.59 ERA, owning 54 strikeouts in 48 2/3 innings.
"We sent him down to get work to get built back up, and he's had consistent work about every third day," Girardi said. "He's been really good."