In the bottom of the eighth, backup catcher Ryan Hanigan pinch-hit for Phillips, who went for X-rays. Results were not immediately available.
"We'll have to wait and see how he's doing [Sunday]," Reds manager Dusty Baker said. "Hopefully, it's not too serious."
In the top of the ninth, a thinned Reds bench forced Baker to make moves he wouldn't ordinarily make. With infielders Alex Gonzalez and Paul Janish already used and removed from the game, Adam Rosales moved from third base to second base. Hanigan became the catcher when Ramon Hernandez moved over to play third base for the first time in his career.
"That's why you do so many unorthodox things, because you don't plan on losing anybody in that situation," Baker said.
Phillips, hitting .275 with seven homers and a team-leading 34 RBIs this season, has been one of the National League's hottest hitters this month. In May, he is batting .350 (28-for-80) with five homers and 27 RBIs.
If Phillips is unable to play in Sunday's series finale vs. the Indians, the Reds have multiple options. Jerry Hairston Jr., Rosales and Janish can all play second base.
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.