Volstad (3-2) didn't allow a hit until pitcher Cole Hamels lined a single to center with two outs in the fifth. The 21-year-old right-hander gave up three hits and walked four in his fifth career start.
Joe Nelson worked the seventh, Arthur Rhodes and Matt Lindstrom combined for three outs in the eighth, and Kevin Gregg finished for his 25th save in 31 chances.
Hamels (9-8) again was a hard-luck loser. The left-hander allowed three runs - two earned - and seven hits in 6 1-3 innings, striking out seven. He hasn't won since July 3.
Despite a 3.35 ERA, Hamels barely has a winning record because of poor run support. He's allowed three runs or less eight times without getting a win, including losses of 1-0 and 2-0. Hamels is 0-4 with four no-decisions in those starts. He has a 3.19 ERA in his last six losses.
The Phillies were second in the NL in runs, but they do most of their scoring in bunches. Philadelphia has scored three runs or less in 39.5 percent of its games, going 9-36.
Florida led 2-0 after six innings. Cody Ross hit a two-out double in the second and scored on Matt Treanor's single to right, and Jeremy Hermida singled and scored on Josh Willingham's two-out double in the sixth.
First baseman Ryan Howard's 14th error contributed to Florida's third run. With two on and one out in the seventh, Howard threw wide to second base on pinch-hitter Mike Jacobs' grounder to first.
Ryan Madson replaced Hamels and Hanley Ramirez drove in a run on a groundout to shortstop for a 3-0 lead.
Volstad breezed through the first four innings, then pitched out of jams in the fifth and sixth. He retired Shane Victorino on a fly to right to leave two on in the fifth.
Volstad got defensive help in the sixth. After Chase Utley led off with a single, center fielder Ross made a headfirst, diving catch on Howard's liner. Geoff Jenkins blooped a two-out single to left, but Volstad got Eric Bruntlett on a slow roller to first.
The Phillies stranded Victorino's leadoff double in the eighth off Rhodes.
Notes: Philadelphia acquired LHP Scott Eyre from the Cubs for a minor leaguer. ... A crowd of 45,521 was the largest at Citizens Bank Park this season and the fifth-most in the ballpark's five-year history. ... The Phillies had homered in 14 straight games. The club record is 16. ... The Marlins didn't hit a homer in the three-game series. ... Utley extended his hitting streak to 11 games. ... Volstad hasn't allowed a homer this season in 124 2-3 innings in the minors and majors.
