The 22-year-old limped off after just one minute of the weekend's game at Loftus Road and could face a spell on the sidelines.
"He went over on his ankle, whether it's ligaments we need to assess but obviously it was sufficiently bad enough for him to come off very early in the game," said assistant manager Kevin Bond.
"That was disappointing. He's been very important for us. I don't know what the prognosis is for that."
Phillips has started 13 games in the Sky Bet Championship for Rangers this season - as well as making a further eight appearances from the bench - following his move from Blackpool last summer.
Rangers were already without top scorer Charlie Austin, defender Danny Simpson and midfielder Alejandro Faurlin through long-term injuries.