The Phillies used their bullpen Thursday, when Joe Blanton could not pitch because of a right elbow injury, so the Phils called up Herndon because they needed a fresh arm in the bullpen.
Philadelphia is expected to place Blanton on the disabled list next week and recall right-hander Vance Worley to take his place in the rotation.
Blanton, who underwent an MRI on Friday, said after the 3-2 win over the Rangers that he was told he has no structural damage to the elbow. He said he will rest the elbow for the immediate future but had no timetable for his return.
"I didn't make anything worse structurally," Blanton said.