Romero was placed on the minor-league DL on Friday due to a sprained oblique, Meghan Montemurro of The Athletic reports.
The Phillies didn't describe a timetable for Romero but it's expected that he will be out a couple weeks while recovering from this injury. Through 18 starts with Double-A Reading, he's logged a 3.80 ERA and 1.30 WHIP with 100 strikeouts in 106.2 innings.