Phillips was returned to Triple-A Louisville on Thursday, Gordon Wittenmyer of The Cincinnati Enquirer reports.
Phillips made two spot starts during his time with the Reds, striking out 10 over 8.2 innings but giving up eight earned runs on 10 hits and six walks. Because he was up with the Reds as a replacement for one of their pitchers that recently landed on the COVID-19-related injured list, the rookie right-hander can rejoin the big club at any time. He'll be a candidate to draw another start next week while the Reds are still without a fifth member of the rotation with Graham Ashcraft (toe) on the 15-day IL.