The Wales scrum-half suffered a reaction in his rehab after a six-month lay-off from knee reconstruction and was told by doctors to rest for two weeks.
Phillips will not play regional rugby before the November internationals but the Ospreys insist he will only make a return when he is fully fit.
Ospreys coach Sean Holley said: "Mike will not play any part in the EDF Energy Cup pool matches and we're now looking at Edinburgh (November 28) at the earliest.
"It would be a huge gamble for him to play before that. He may play some club rugby but he will not start jogging until next week.
"He underwent a traumatic operation in the summer and we don't want to rush him back after this set-back. He has to be 100 per cent."
EDF Cup champions Ospreys kick-off against Harlequins at the Liberty Stadium this Sunday.
Gavin Henson is in the 22-man squad after emerging unscathed from his return from injury last week, but Wales forwards Jonathan Thomas and Ian Evans are rested.
Ospreys (from): Lee Byrne, Tommy Bowe, Johnny Vaughton, Shane Williams, Sonny Parker, Gavin Henson, James Hook, Daniel Biggar, Rhys Webb, Duncan Jones, Adam Jones, Andrew Millward, Huw Bennett, Richard Hibbard, Ian Gough, Lyndon Bateman, Alun Wyn Jones, Ian Evans, Steve Tandy, Tom Smith, Ryan Jones, Marty Holah, Filo Tiatia.
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