Kelly Johnson added solo shots in the fifth and seventh innings, Chris Snyder also connected in the fourth and Kris Benson threw six-plus strong innings for the Diamondbacks, who won for the second time in three games.
Benson (1-1) allowed the three runs - two earned - on eight hits with five strikeouts. Chad Qualls recorded an out for his third save in five chances.
Shane Victorino was 2 for 5 with a triple and an RBI single for the Phillies.
Reynolds and LaRoche helped the Diamondabcks rally from an early 2-0 deficit.
Justin Upton singled with one out and Reynolds hit his team-best sixth home run a half-dozen rows into the left-field stands off Cole Hamels (2-2) to tie it. LaRoche followed with his first Diamondbacks home run. Snyder had a two-run, two-out shot over the left-field bullpen to make it 5-2.
Kelly Johnson led off the fifth with his fourth home run just over the left-field fence to give Arizona a 6-2 lead.
Hamels allowed six runs on eight hits over six innings with a walk and seven strikeouts.
Brian Schneider singled leading off the seventh against Benson and scored on Placido Polanco's grounder to third off Leo Rosales to cut the Diamondbacks lead to 6-3.
Johnson added his second home run, a lined shot just to the right of the Phillies' bullpen in right field off J.C. Romero, to make it 7-3.
Hamels hit a one-out double and Victorino tripled to the center-field wall to give Philadelphia a 1-0 lead in the third.
The Phillies extended their lead to 2-0 in the fourth on an unusual play.
Jayson Werth hit a towering fly ball to the right-center field corner that Chris Young appeared to catch, only to fumble the ball to the ground as he attempted to pull it out of his glove. Werth, who was between first and second when Young dropped the ball, raced home.
Young was charged with a four-base error, his first error since August 9.
Diamondbacks manager A.J. Hinch argued with crew chief Dale Scott for several minutes before he was ejected and another couple of minutes after.
NOTES: Arizona's five home runs were one short of the franchise mark and were the teams most since hitting five on April 6, 2009, against Colorado. Johnson has two two-homer games this season and six in his career. The Diamondbacks' three-homer fourth was their second of the season and 17th in franchise history. Hinchs ejection was the fourth of his career. Phillies RHP Joe Blanton started for Double-A Reading Friday in his second rehab assignment, allowing four hits and one walk over three scoreless innings with three strikeouts. Closer Brad Lidge, making his seventh rehab appearance, came on in relief of Blanton and allowed one hit and one walk in an inning. Blanton is on the disabled list with a strained left oblique while Lidge is recovering from surgery on his right elbow.
