The team said Oswalt went back to make sure his wife and daughter were safe and that there wasn't any significant damage to his home. His parents' home was destroyed by a tornado a year ago.
No timetable has been set for his return, though the Phillies were hopeful he'd be back for his next start.
Oswalt left the team before Wednesday's game against Arizona, a day after leaving the clubhouse early following a rough outing against the Diamondbacks. The right-hander allowed five runs and six hits on three innings to see his 10-game winning streak end.