De Los Santos will be called up to start Sunday against the Marlins, Matt Breen of The Philadelphia Inquirer reports.
The Phillies will need a spot starter again with Zach Eflin hitting the disabled list with a blister. De Los Santos had a solid performance in his big-league debut Tuesday, picking up a win and a quality start against the Mets. Eflin isn't expected to miss more than one start, but if De Los Santos keeps pitching well the Phillies will eventually be forced to find a role for him.