Phillips left Tuesday's game against the Padres entering the eighth inning with a strain in his left calf, and he didn't play at all Wednesday, Thursday or Friday.
Reds manager Dusty Baker had Phillips starting until about 20 minutes before opening pitch.
Baker had expressed earlier in the day that he felt Phillips was ready and said it was "hell" trying to keep Phillips out of the lineup Friday night.
"You never really know," Baker said at the 4 p.m. ET manager's interview Saturday. "But [Phillips] knows how to play smart. He did it earlier in the year when he had a worse injury."
Entering Saturday, Phillips was batting .296 with 13 home runs and 62 RBIs this season and has been an instrumental part of the Reds' offense in the absence of Joey Votto. He is hitting .339 with three homers and 13 RBIs since Votto left the lineup.
On Friday, Baker said Phillips would be available to pinch-hit if needed.
Wilson Valdez started in place of Phillips.