Phillips limped off after just one minute of Saturday's 3-3 draw with Burnley 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."
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