Roy Halladay went through a vigorous bullpen session Tuesday before the Phillies played the Mets. Philadelphia pitching coach Rich Dubee said the right-hander threw 56 pitches, stopping to simulate rest between innings. He could have several more bullpen sessions before pitching a few simulated games. Halladay has been out since May 28 because of a strained latissimus dorsi muscle on the right side of his back.