The triumph may offer some vindication for the Astros, whose lone 2017 World Series title was tarnished in the eyes of many by the sign stealing scandal.
Astros manager Dusty Baker secured his first-ever World Series title in his third appearance, having won 2,093 MLB games, nine divisional titles and three pennants.
Starting pitcher Framber Valdez was outstanding with nine strikeouts across six innings, allowing only two hits and one earned run.
Schwarber's solo shot over right field was his sixth homer of the postseason. It came after Valdez had given up only one home run all regular season to left-handers.
But the Astros rallied immediately with Phillies starter Zack Wheeler, who was brilliant with five strikeouts, pulled after Jose Altuve and World Series MVP Jeremy Pena got on base. Alvarez crushed reliever Jose Alvarado's fourth pitch beyond the hitter's backdrop over center-field for a 450-foot three-run blast.
Alvarado struggled to regain his composure, with designated hitter Christian Vazquez driving in Alex Bregman for a fourth run.
The Astros' sixth-inning rally seemed to suck the life out of the Phillies who had led the World Series 2-1.
The triumph capped an 11-2 postseason for the Astros, who had competed in four of the past six World Series.