"Casper is someone that we've had our eye on since Spring Training," Phillies general manager Ruben Amaro Jr. said in a statement. "He's a versatile outfielder who adds depth to our club and can be a power threat off the bench."
Wells has hit .236 with 25 home runs, 81 RBIs and a .712 OPS in 732 plate appearances over four seasons with the Tigers, Mariners, A's and White Sox. He can play all three outfield positions.
He will join the team this weekend in Washington, where the Phillies play the Nationals. A corresponding move will be made at that time.