Erik Kratz and Domonic Brown each homered off Koehler, and the Phillies rolled to a 7-2 victory over Miami.
The Phillies used the long ball to overcame a two-run deficit and snapped the Marlins' three-game winning streak.
Delmon Young added a third Philadelphia home run, providing all the support Kyle Kendrick needed in his complete-game victory.
"It was a good game the first four innings," Marlins manager Mike Redmond said. "In the fifth and sixth, they put up some good at-bats, and we couldn't hold them down. They got a couple of big hits, big home runs. That fifth and sixth, we just couldn't overcome. They got the big hits tonight, we didn't."
After sweeping the Mets in three games at Marlins Park, the Marlins entered their-six game road trip with some energy. They took an early two-run lead, but at Citizens Bank Park, they also saw that wasted chances can come back to haunt you.
"The Phillies, they've got guys who can put it in the seats rather quickly," Redmond said. "I've seen some big numbers put up in this ballpark. They have the ability to hit those home runs. We have to string together multiple hits to score runs."
Koehler, who gave up five runs (four earned) in five-plus innings, started off with four scoreless frames, but in the fifth, the Phillies seized control with three runs, two of which were earned. Kratz homered to open the inning, and Kendrick, Philadelphia's starting pitcher, delivered his first Major League triple. He scored on Ben Revere's single. Revere's stolen base, coupled with catcher Rob Brantly's throwing error, set up the go-ahead run.
"Poor execution of pitches mixed in there," said Koehler, who fell to 0-4 while still searching for his first Major League win. "There were two situations where I had a guy 0-2 and didn't put him away, and ended up leaving a pitch on the plate and they did what they're supposed to do."
Cesar Hernandez's RBI grounder to first pushed across the third run.
In the sixth inning, the Phillies put up four runs, with two charged to Koehler.
Ryan Howard doubled to open the sixth, and Brown belted a two-run shot to right, ending Koehler's day. The Phillies weren't done, as Young immediately homered off Ryan Webb, marking the sixth time this season Philadelphia has gone back-to-back.
Brown and Young have hurt the Marlins all season. Four of Brown's 17 homers have been against Miami, compared to three of Young's five blasts.
"A home run is the greatest hit in baseball," Phillies manager Charlie Manuel said. "That's what a home run is. The crowd loves home runs. It's a great way to score runs."
The way Brown has had his way with the Marlins all season has Redmond reconsidering how to approach the young slugger.
"A guy like that, we've got to pitch around him," Redmond said. "We're throwing him a lot of breaking balls. When you're going good like that, we make a mistake and he hits it. It just seems like the way he's going right now, he's locked in, he's hitting everything. You've got to pitch him better."
Brown's homer capped an eight-pitch showdown with Koehler, and he blasted a high changeup.
"He fouled off some good curveballs in that at-bat, and I floated a changeup up there," Koehler said. "Catchers don't usually catch high changeups. You don't want to get beat there with that pitch. But at the same time, that's what he's supposed to do."
In defeat, Marlins players extended a couple of streaks.
Chris Coghlan's second-inning double extended his hitting streak to 10 games. And with a single and a walk in his first two plate appearances, Ed Lucas had a string of reaching base safely seven straight times, which ended with an eighth-inning lineout.
Lucas was 4-for-4 with two walks in Sunday's 11-6 win over the Mets.
Lucas' walk was instrumental in Miami's two-run third inning off Kendrick.
Juan Pierre singled with one out, and Lucas drew a walk. Derek Dietrich's RBI single to right opened the scoring, and Marcell Ozuna's smoked grounder that deflected off Freddy Galvis' glove at third base produced the second run.
"We don't have a home run-hitting team," Redmond said. "When we get a guy on third, we have to take advantage of that because we're not hitting a lot of home runs."