Oswalt, who is 3-1 with a 3.33 ERA in five starts, had been on the DL with lower back inflammation. He made one rehab start for Class A Clearwater, allowing three earned runs on seven hits in five innings with five strikeouts.
Oswalt will be on a pitch limit in his first start back. Manager Charlie Manuel said Monday the club preferred Oswalt build his endurance at the major league level.
Right-hander Vance Worley was optioned to Triple-A Lehigh Valley.