The Phillies have won six out of seven and they concluded a three-game sweep of the Nationals.
The first seven Philadelphia batters reached base in the third, driving Washington starter John Lannan (2-4) from the mound.
After another double from Raul Ibanez scored Howard and Mayberry, Wilson Valdez singled in Ibanez with the final run of the inning. Ibanez also had a solo homer in the fifth.
Halladay (5-1) gave up two runs on six hits over seven innings. He has 57 strikeouts this season in 53 1/3 innings.