The scrum-half has been ruled out for three to four months after damaging ankle ligaments.
That injury is almost certain to keep him out of Wales' Six Nations clashes with England, Scotland and France in February.
But there is now increasing concern among the Ospreys management that Phillips, who was one of the Ospreys stand-out performers last season, may be out for even longer.
And that would leave Wales' first-choice number nine as a major doubt to be fit for the final ties with Ireland and Italy in March.
"Mike's return is off the radar and we're looking at three to four months. I don't know if he'll see any of the Six Nations," admitted Ospreys coach Sean Holley.
"My focus is on this Saturday and then the European ties. But I know he's not going to be available at any point in 2009.
"We get updates every day but with Mike it has been a very quick one. We have to work like that, we have to have priorities."
Phillips, 27, suffered the injury when he limped off in the Welsh region's European Cup win over Clermont Auvergne in October.
His absence has led to a scrum-half crisis at the Liberty Stadium, with back up No9 Shane Williams the latest to succumb to injury.
South African international Ricky Januarie could be thrown into emergency action against Munster on Saturday despite only arriving in the UK this week.
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