Phillips passed his SCAT 2 concussion tests, which check his balance, speech and memory.
"He did very well. He told me he was doing better today," head athletic trainer Paul Lessard said. "I'm sure he had a mild concussion. That's the way I'm treating him."
However, Lessard noted that Phillips' symptoms were not severe enough to warrant a stint on the seven-day disabled list specifically for concussions.
Phillips exited early from Wednesday's game vs. the Brewers when he felt dizzy after taking a shot to the head from a sliding Aramis Ramirez as he was caught stealing second base. Less than an hour before Thursday's series opener, he was scratched when he showed to be less than 100 percent while hitting and taking ground balls.
"He got 100 today and got a 90 yesterday," Reds manager Dusty Baker said of Phillips' tests. "He was trying hard to lobby to get back in the lineup. As long as he passed the test and the trainer said it was OK, that's all it took."