Heisey took Mariners starter Randy Wolf deep with a two-run blast in the first and added another two-run shot in the fifth off reliever Logan Bawcom, giving him three home runs on the spring.
"I was able to take advantage of two mistakes today, and that's really the name of the game when you're up there," Heisey said. "These guys, when they're making their pitches, it's tough to get hits. But you have to be able to take advantage of the mistakes."
Phillips went 2-for-2 with three RBIs for the Reds as the veteran second baseman lifted his Cactus League batting average to .267 in six games.
Wolf, making his second start of the spring for Seattle, allowed four runs in three innings of work. The veteran southpaw didn't pitch last season as he recovered from Tommy John surgery. He threw two scoreless frames in his debut, but was tagged for two home runs and a triple by the Reds and also walked two.
Wolf said he struggled with his curveball and a new splitter he's working on, but he was encouraged that his arm felt strong as he continued his comeback. The veteran was kicking himself for a pair of two-out walks, but otherwise said the "awful results" weren't indicative of how he felt on the mound.
"When you feel good, that's an encouraging thing, especially with what I went through the last year and a half," Wolf said. "Of course, especially in Spring Training, people get really caught up with results. The ironic thing is I think I feel better this time than my last time out."
Heisey's first blast, on the heels of a walk by Phillips, gave Cincinnati a quick 2-0 lead. Kristopher Negron laced an RBI triple in the second, and Phillips added his solo shot in the third to make it 4-0.
The Reds took an 8-0 lead in the fifth on a two-run single by Phillips and Heisey's second long ball to left.
But Seattle scored three runs in the bottom of the fifth and five more in the sixth to tie the game, with Peterson hitting his first home run of the spring as a callup from Minor League camp.
Peterson went 2-for-3 in his second straight game with the big league club and is 3-for-6 in three Cactus League games.
The Mariners also got an RBI double from Stefen Romero, a two-run double by Cole Gillespie and an RBI double by Jesus Montero in the sixth off Reds right-hander Daniel Corcino, who pitched in Triple-A last year. Gillespie added an RBI single in the eighth to give him three RBIs.
Brett Marshall, a 23-year-old right-hander, gave up four hits and walked three in his second spring start for the Reds, but managed to keep the Mariners off the scoreboard. Marshall struck out four batters in his 53-pitch outing, including Dustin Ackley to escape a bases-loaded jam in his final frame.
Up next: A possible candidate for the rotation if Mat Latos isn't ready, Alfredo Simon has performed well by not allowing a hit over his first five innings in two games, with four strikeouts. Simon will make his third start of the spring on Saturday, when the Reds face the Cubs in Goodyear at 3:05 p.m. ET, live on Gameday Audio. Manny Parra and Sam LeCure are also scheduled to see action. Jason Hammel is the Cubs' probable starter.