Roberson, 28, spent most of last season with AAA Ottawa, where he batted .266 in 113 games playing primarily in center field. In two recalls by the Phillies in 2007, Roberson batted .286 (8-28) in 28 games.
A switch-hitter, Roberson was drafted by the Phillies in the 9th round of the 2001 First-Year Player Draft and made his major league debut in 2006. He was named the Phillies' best minor league player and Eastern League rookie of the year in 2005 after batting .311 with AA Reading.
To make room for Roberson on the 40-man roster, OF Jeff Fiorentino was designated for assignment by the Orioles. Fiorentino, who hit .253 in brief stays with the Orioles in 2005 and 2006, batted .282 with 15 homers and 65 RBI at AA Bowie this past season.