De Los Santos was called up from Triple-A Lehigh Valley on Friday.
De Los Santos made two appearances during his first stint with the Phillies this season, allowing two runs on four hits with five strikeouts over three innings. The 23-year-old has pitched well for the IronPigs with a 2.37 ERA, 1.16 WHIP and 26:7 K:BB and could serve as a long-relief option for the Phillies.