Although the bulk of his career came with the Toronto Blue Jays, Halladay left a big impression in Philadelphia over his four seasons with the Phillies.
He went 55-29 with a 3.25 ERA in 103 starts. The right-hander won the National League Cy Young Award in 2010 and was runner-up in 2011, and he threw a no-hitter in the opening game of the 2010 NLDS against the Cincinnati Reds.
"Roy Halladay made an indelible mark on Phillies history with so many spectacular moments, including his perfect game and postseason no-hitter," executive vice president David Buck said of Halladay in a statement. "His impact on the game was evident by his induction into the Hall of Fame. We are honored to have Roy join an elite group of players to have their numbers retired by the Phillies."
Halladay died in a plane crash in November 2017.
He was enshrined as a Hall of Famer on the first ballot in 2019. His plaque doesn't feature the Blue Jays or Phillies logo. His family explained the bond he enjoyed with each franchise made it impossible to choose one over the other.
The Blue Jays retired Halladay's No. 32 jersey in March 2018.
Philadelphia will also unveil a statue of the eight-time All-Star as part of his jersey retirement ceremony.