The club announced on Thursday it had designated Robertson for assignment, following his effort on Wednesday in a 10-6 victory over the Florida Marlins at Citizens Bank Park. The Phillies had a 10-0 lead when Robertson entered the game in the eighth inning. He allowed six runs in just two-thirds of an inning, which ultimately forced manager Charlie Manuel to use Ryan Madson in the ninth inning.
Robertson went 6-8 with a 5.47 ERA in 19 appearances this season with the Marlins, and 2-1 with a 9.45 ERA in six appearances with Triple-A Memphis, the Cardinals' affiliate, before the Phillies signed him.
The Phillies replaced Robertson on the 40-man roster when they claimed right-hander Cesar Carrillo off waivers from the San Diego Padres. Carrillo, who is not joining the Phillies, went 5-14 with a 5.60 ERA in 27 starts this season with Triple-A Portland.
The Phillies also placed right-hander Scott Mathieson on the 15-day disabled list with a strained latissimus dorsi. Mathieson last pitched Sunday against the Milwaukee Brewers.
Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.