De Los Santos was recalled from Triple-A Lehigh Valley to serve as the 27th man for Friday's doubleheader against the Mets.
The right-hander had a two-day stint in the majors in mid-June, and he'll rejoin the big-league roster for Friday's twin bill. De Los Santos has appeared in four games for the Phillies this season and has allowed three runs on four hits with four strikeouts and a walk over three innings.