Hammer was optioned to Triple-A Lehigh Valley on Saturday.
Hammer has a solid 3.79 ERA in 19 innings with the Phillies this season, but the underlying numbers don't come close to supporting that figure. Both his 16.1 percent strikeout rate and 14.8 percent walk rate are quite poor. He'll make way on the roster for Mike Morin, acquired in a trade from the Twins on Saturday.