The Cardinals (39-21) lead the Reds (36-24) by three games in the NL Central after beating Arizona 12-8 on Thursday, hitting a season-high five homers. Matt Holliday went 2 for 3 with a two-run shot in the first.
David Freese extended his career-best hitting streak to 16 games for St. Louis, which had dropped three of its previous four.
The Reds have lost three of four, falling 12-4 to Colorado on Wednesday. Cincinnati didn't score after Xavier Paul hit a three-run homer in the first inning.
The Reds have played each game in that stretch without Phillips, who has been dealing with a bruised left forearm. He expects to return Friday against a St. Louis team that has won four of the six meetings with Cincinnati this season.
"I feel like the Cardinals are the best team in baseball right now," Phillips told the team's official website. "Those are the type of teams we have to step our game up, and I'm glad I'm going to play Friday. I think everybody on our team is looking forward to it. That shows where you really are when you play against the best teams."
They'll also face one of the top pitchers in the game, as Wainwright (8-3, 2.33 ERA) has been especially good of late.
The right-hander won his third straight start and registered his third complete game of the season Saturday, giving up one run and striking out 10 in a 7-1 victory over San Francisco. He's 4-1 with a 1.83 ERA in his last five outings.
Wainwright has walked six this year, making his 14-to-1 strikeouts-to-walks ratio by far the best in the majors. No pitcher has finished with a better ratio than Bret Saberhagen's 11 to 1 in 1994.
"You can go a tick or two down in velocity and locate and still get the job done,'' Wainwright said.
Victories have been difficult to come by for Wainwright against Cincinnati lately, though. He allowed two runs in seven innings of a 2-1 defeat April 29 and has gone 1-4 with a 4.34 ERA in his last five starts versus the Reds.
Leake (5-2, 2.75) has been even better than Wainwright recently, going 3-0 with a 0.33 ERA while allowing one earned run in 27 innings over his last four starts.
The right-hander, who went 2-2 with a 4.32 ERA in his first seven outings to spark rumors that he might lose his spot in the rotation, pitched six innings to beat Pittsburgh 2-0 on Saturday.
"When I start hearing I'm going to lose my spot, part of me says don't worry about it and part of me says get a little attitude going," Leake said.
Leake has yet to face the Cardinals after going 1-1 with a 3.38 ERA in three starts versus St. Louis last season.
Holliday went 0 for 4 in St. Louis' 4-2 victory in the last matchup May 1, snapping his 14-game hitting streak versus the Reds.