The Queens Park Rangers player, a £5m summer signing from Blackpool, was hurt six minutes into Saturday's 3-3 draw with fellow Championship promotions hopefuls Burnley.
"It looks quite long term," said Harry Redknapp, the QPR manager, after Phillips had a scan on the injury. "We'd hope to get him back this season, I wouldn't know whether we will or not. He's got a few problems with his ankle and is struggling at the moment. It's a serious one."
Phillips' lay-off is a set-back for Scotland manager Gordon Strachan ahead of next month's friendly in Poland, with Sunderland striker Steven Fletcher also a major doubt with an Achilles problem.
A hamstring strain kept twice-capped Phillips out of the national squad for the November friendlies against the USA and Norway.