Phillips was contracted with the Ospreys until the end of the 2013/14 season, but following this agreement, he is free to join French Top 14 club Bayonne. Phillips spent four years at the Liberty Stadium, during which time he made 60 appearances and scored five tries.
Ospreys Rugby would like to wish Mike the best of luck in his future career.
Phillips added: “I have had a great time at the Ospreys and am grateful for their assistance in developing my career. They are a region with a great squad of players and great supporters, and I wish the region all the best for the coming seasons.”
