On a 3-1 pitch, Phillips connected for his second homer of spring, easily clearing the left-field fence.
Chien-Ming Wang pitched scoreless sixth and seventh innings with one hit allowed to get the win.
Oakland took a 2-0 lead in the first inning following a two-out error by the Reds. With runners on first and second base against starter Tony Cingrani, Derek Norris hit a pop up near the first-base dugout, where first baseman Joey Votto and catcher Devin Mesoraco converged to make the catch. As they collided, the ball bounced out of Mesoraco's glove. Still alive, Norris followed by ripping a two-run double to the center-field wall.
With two outs in the bottom of the first against Sonny Gray, Votto went to the opposite field on a 2-2 pitch for a solo homer over the fence in left field. It was Votto's first homer of the spring. Cincinnati added two runs in the second inning on RBI singles by Mesoraco and Hamilton.
A two-run bottom of the fourth inning began with three straight hits off of Gray. Skip Schumaker's RBI single was the third hit and chased the right-hander.
The possible A's Opening Day starter, Gray gave up five runs (three earned) and six hits over three-plus innings. He walked two and struck out four.
Cingrani gave up five runs (three earned) on three hits and three walks over four-plus innings. He gave up three of his runs in the fifth after beginning the inning with back-to-back walks. Jake Elmore hit an RBI single to left field, and Cingrani was done after he balked in a run and allowed Billy Burns reach first on a strikeout due to a wild pitch. A sacrifice fly by Alden Carrithers against Lee Hyde made it a 5-5 game.
Up next: Scott Kazmir will make his third start of Spring Training on Monday against the Cubs at 1:05 p.m. PT (listen to an exclusive webcast).
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.