They also fell to 77-79 overall, and need to win four of their final six games to avoid following their first playoff season in a generation with a losing 2009.
"We had a little run at the end today and ran out of steam," Brewers manager Ken Macha said.
Coming off an outing against the Cubs in which he slipped into a 6-0 deficit before recording the second out of the second inning, Bush fared only slightly better against the Phillies, who took a 4-0 lead through two innings. Bush (5-9) was charged with five earned runs on nine hits in 4 1/3 innings.
In the first, Jimmy Rollins hit his 33rd career leadoff home run and Ryan Howard matched Fielder atop the Major League leaderboard at 137 RBIs with a double. In the second, Phillies pitcher Joe Blanton was squared to bunt when a Bush curveball struck him in the leg, and two batters later Shane Victorino delivered a two-out, two-run double. The Phillies tacked on two more runs in the fifth inning against Bush and reliever Josh Butler, who made his final Brewers appearance before leaving for the Arizona Fall League.
Bush, who spent two months on the disabled list earlier this season and said he's been disappointed by the velocity of his fastball, is supposed to make one more start on Saturday in St. Louis. Mark him in pencil for now.
"He says he feels fine," Macha said. "We'll sit down and talk with him. I don't think he really wanted to come out of [Sunday's] game, but I thought I made that decision for him."
Bush said he wants to make that last start. He threw just 80 pitches against the Phillies.
"I really don't know [about pitching again]," Bush said. "We haven't sat down and discussed anything yet. The rest is going to be good for me, no doubt about it. Since I got hurt, it's been a battle to feel completely healthy, so I'm sure that having a couple of months off and some time without throwing at all is going to be beneficial. Let my arm heal, let everything rest. I look forward to coming back in the spring feeling normal again. As for the last week of the year, I don't know. We haven't discussed that yet."
Until Gamel's homer in the sixth, Blanton (12-7) had allowed only one run on six Brewers hits. As he rounded the bases, Gamel allowed himself a little fist pump. It was his fifth homer this season, but before that at-bat he was 1-for-8 with five strikeouts since returning for September.
"I was saying some things to myself that I probably can't say to y'all," Gamel said. "That felt good, definitely. I'm sure it made [hitting coach Dale Sveum] feel good, too, after the adjustments we had been making the last three or four days. We kind of figured out what was giving me problems."
Corey Hart followed two batters later with an RBI single, and two batters after that Fielder batted representing the go-ahead run. Philadelphia reliever Sergio Escalona retired him on a first-pitch groundout to preserve a 6-5 lead.
The Phillies won despite leaving the bases loaded in the fourth, fifth and sixth innings, and their magic number to clinch the National League East fell to three.
The Brewers have been out of postseason contention since Tuesday, but a crowd of 37,197 on Sunday pushed the Brewers' season attendance to 3,037,451, second-best in club history to last year's record.
"I've enjoyed my year here. These fans have been fantastic," Macha said.
The Brewers saved a number of their highlights for home. They won the home opener when Rickie Weeks beat a throw home in the bottom of the ninth. Casey McGehee had an exciting sixth inning on June 30, when he dropped a routine pop-up in the top of the frame, but atoned in the bottom half with his first career grand slam. A month later, on July 30, McGehee provided an emotional moment when he hit a go-ahead, pinch-hit homer on the night his young son, who has cerebral palsy, threw the first pitch. Yovani Gallardo picked a home game to become the fourth Brewers pitcher to reach 200 strikeouts, and Fielder broke both the franchise RBI record and walks mark in games at home.
The Brewers hit both of their walk-off home runs at home in September games against contenders. Fielder hit his Sept. 6 to beat the Giants and Ryan Braun hit one against the Phillies on Saturday.
"The expectations were off the charts and I had the same expectations as the fans did," Macha said. "Not getting to where you wanted to go, that's a disappointment."