SAN FRANCISCO - As the Phillies and Giants traded runs in the later innings Sunday, the Phillies shuttled relievers back and forth from the dugout to the bullpen in foul territory at AT&T Park. A few warmed up, then sat. Then warmed up again.

An 8-7 loss was sealed with Severino Gonzalez on the mound for his second inning of work. The bullpen has endured the brunt of the workload in recent weeks, and the unit looks spent.

That is why the Phillies will transition Adam Morgan from the rotation to the bullpen beginning Monday. The team optioned lefthander Elvis Araujo to triple-A Lehigh Valley.

Vince Velasquez will be activated from the disabled list Monday to start at Arizona.

In their last 18 games, the Phillies have had just one starting pitcher last seven innings. That was Jeremy Hellickson on June 20. Phillies manager Pete Mackanin has been forced to rely on his relievers.

On Sunday, he opted for another inning of Gonzalez rather than Hector Neris.

"I stuck with him because I'm going to the bullpen so much that I have to be careful with all of my pitchers," Mackanin said. "I can't use everybody the way I want to every night."

Brett Oberholtzer, David Hernandez and Gonzalez each allowed runs Sunday. Hernandez has a 14.21 ERA in his last six appearances.

"He hasn't pitched as well as he was pitching earlier," Mackanin said. "He's better than he's pitched lately. It's always a question of location, putting the ball where you want to put it."

Morgan, for now, will be used as a swing man. He has just one career relief appearance, in 2012 with single-A Clearwater.

"We're going to get a look at him in that role for the time being, which doesn't mean he's never going to start again for us," Mackanin said. "But at this point we want to give it a look to see if he can pitch out of the bullpen."

Extra bases

Odubel Herrera homered in the seventh inning to match his home run total (eight) from a season ago. The Phillies had him practice in right field Saturday, but Mackanin said there is no current plan to move Herrera from center field, where he has committed more mistakes this season than last. . . . The Phillies have not won back-to-back games since May 17-18. . . . Jeanmar Gomez saved 20 of the team's first 32 wins, which made him the fastest Phillie to 20 saves in club history. . . . Velasquez will face Diamondbacks lefthander Robbie Ray on Monday as the teams open a three-game series at Chase Field.