Friday's blast came in the sixth inning against Giants right-hander Tim Lincecum.
"I feel pretty good right now," said Franco, who is 7-for-17 with two doubles, three home runs and seven RBIs in his last four games. "I'm trying to make good contact. I was looking for a slider there because I know he throws soft. I was just looking for everything because the fastball was 86, 88 mph. I'm pretty feeling comfortable right now."
But Phillies right-hander Luis Garcia surrendered a solo homer to Buster Posey in the top of the seventh to stop the momentum.
The lack of shutdown innings has been a problem for the Phillies this season. They score a run or two, but the pitching staff gives up a run or more the following inning.
"Not able to put a zero up," Phillies manager Ryne Sandberg said. "Yeah, that's been a problem, at least the last two games as far as allowing us to get runs, have a lead and try to add onto that. That's been a problem."
Garcia seemed baffled at what happened in the seventh. He threw Posey a 2-0 four-seam fastball, but the pitch inexplicably had some sink to it.
"That's happened twice," Garcia said. "It happened once in Colorado, too. A fastball outside and the ball sinks."
Left-hander Elvis Araujo allowed an inherited runner to score in the fifth inning. The Phillies bullpen entered the night allowing 46 percent of their inherited runners to score, which was the worst mark in baseball.
Todd Zolecki is a reporter for MLB.com. Read his Phillies blog The Zo Zone, follow him on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.