The source, who declined to be identified, said Phillips, New Zealand back row Dwayne Haare and fly-half Stephen Brett were intoxicated when they arrived at the session on October 11.
Phillips was suspended for 10 days last year for an off-the-pitch misdemeanour following a defeat by Toulouse.
The British and Irish Lion has been named in the Wales squad for the November tests against South Africa, Argentina, Tonga and Australia.
- Dwayne Haare
- Stephen Brett