The 25-year-old right-hander yielded one hit and one walk over five scoreless innings in the Dogs' 3-1 loss to the visiting Mesa Solar Sox. Phelps fanned three.
A Notre Dame product who went 6-6 with a 3.19 ERA in 18 starts for Triple-A Scranton/Wilkes-Barre during the regular season, Phelps was 0-2 with a 7.43 mark while allowing a .339 average against in his first four Fall League outings. He was much more effective against the Solar Sox on Monday.
"I was mixing my pitches up really well and keeping hitters off balance today," Phelps said. "I was able to get ahead and put hitters away in good counts."
Phelps delivered first-pitch strikes to 12 of the 17 batters he faced, with 41 of his 67 pitches overall going for strikes.
"It's been enjoyable playing out here and I've been learning a lot. [In Triple-A,] a lot of hitters have big league experience and are a little more patient in their at-bats. A lot of the younger prospects [in the AFL] are more aggressive at the plate," he said.
"I've been trying to attack hitters and it worked out well."
Fellow Yankees prospect Ronnier Mustelier gave Phoenix a 1-0 lead with a leadoff blast in the second inning, but that was all the run support the Desert Dogs gave Phelps.
After his exit, Mesa tied the game in the seventh when Junior Lake (Cubs) tripled and scored on a sacrifice fly by Joe Mahoney (Orioles). The Solar Sox went ahead in the eighth inning on a two-RBI double off the bat of Brian Dozier (Twins).
The Solar Sox and Desert Dogs mustered just five hits apiece, although seven of the 10 combined hits went for extra bases. Together, the teams went 1-for-15 with runners in scoring position. Mahoney was the only batter to collect two hits.
Solar Sox starter Gerrit Cole, the top overall pick by the Pirates in the 2011 Draft, allowed one run on three hits while striking out three over three frames. The Mesa bullpen was masterful, as five pitchers combined to hold Phoenix to just two hits over six innings.
Twins prospect Brett Jacobson (1-2) notched his first victory with a scoreless seventh before Minnesota teammate Dakota Watts fired a pair of perfect frames to notch his second save.
Yankees bullpen prospect Dan Burawa fell to 1-4 after allowing two runs on two hits and a walk in the eighth.
John Parker is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.