The 30-year-old Australian initially arrived on a short-term deal in September but was kept on for the rest of the campaign - going on to make 11 appearances.
However scrum-half Phibbs has been informed that his contract will not be renewed at the end of the season.
Joining Phibbs in leaving will be academy youngsters Herbie Stupple, Jon Vickers, Addison Lockley, Charlie Walker-Blair and James Lightfoot-Brown, while John Andress (Worcester), Bryan Rennie (Bristol), Peter Short (retired) and Chris Bentley (retired) have already confirmed their future plans.
Chiefs head coach Rob Baxter said: "There are tough calls all the time, especially with guys who are good players. Any of these guys moving on is sad but it's also a reality of professional sport that you have to look to keep moving on otherwise you become stagnant.
"They are all moving on or being released for different reasons. Some have different challenges or contracts that they're looking forward to, others because them coming out of contract gives us a bit of flexibility in the budget.
"I'm sure a fair few of the academy guys will go into the Championship and that's probably the best thing for them at the moment - getting as much rugby in a really good team environment and see if they can push on from there.
"We look at the Championship a lot and anybody who performs well in the Championship will be of interest to us."
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