Stumpf was recalled from Triple-A Toledo on Friday.
Stumpf has pitched decently at Triple-A this season, compiling a 3.38 ERA and a 26:5 K:BB over 21.1 innings in relief. He'll provide much-needed depth in a bullpen which only has one other left-handed arm in Blaine Hardy, but Stumpf will likely be used exclusively in low-leverage situations after posting a 10.80 ERA over seven appearances with the Phillies last year.