Moyer, 49, designated for assignment
The 49-year-old left-hander became the oldest player in major league history to record a win in April, but has mostly struggled in 10 starts this season.
Moyer has allowed 34 runs in 53 2/3 innings on the mound for a career-worst 5.70 ERA with at least 50 innings pitched.
"I just felt like that by sending him out there, we were compromising him and the team," Rockies manager Jim Tracy said, according to The Denver Post. "It's difficult, because he's as professional as any player I've ever been around.
"But we felt like this is something we had to do."
According to The Post, by designating Moyer for assignment, the Rockies have 10 days to either trade or release him. He is still owed approximately $500,000 in salary this season.
Moyer earned a spot in the Rockies' rotation during spring training after sitting out for the entire 2011 season due to Tommy John surgery.
Moyer appeared in 19 games for the Phillies in 2010, amassing a 4.84 ERA. The Sellersville, Pa., native won a World Series title as a member of the Phillies in 2008.
Moyer has a lifetime 4.25 ERA through 25 seasons with the Cubs, Rangers, Cardinals, Orioles, Red Sox, Mariners, Phillies and Rockies. His 269 wins rank 35th all-time among big league pitchers.