The former Wales international, who started his career with Scarlets, retired at the end of last season after a spell with Sale Sharks.
However, Scarlets have turned to him as cover ahead of their trip to South Africa where they face Southern Kings on Sunday and Cheetahs on December 2.
The Welsh region were struggling for options at number nine due to injuries and international commitments, and head coach Wayne Pivac believes Phillips will provide some much-needed experience.
Pivac said: "It's just been one of those things. We looked at the nines available to us within the region, and Welsh qualified players in the Championship, but they were unable to travel due to work commitments and club commitments.
"We are delighted that Mike has been able to answer the call and will be joining us in South Africa. He has a wealth of experience, is a proud former Scarlet and will be a great addition to our travelling squad."