The strapping 20-year-old comes in for injured Cardiff No 9 Ryan Powell, joining eight Scarlets team-mates in the 30-man squad.
"We rate him very highly and think he's the next cab off the rank in terms of scrum-halves," national coach Steve Hansen said.
"When he fills out into his full potential, he'll be a very strong halfback in the mould of New Zealand's Justin Marshall."
Phillips has long been touted as an international and his 6ft 3in frame could come in handy as Wales look to end their run of six Test losses against two of the heavyweights of world rugby.
Llanelli co-coach Nigel Davies added: "He's a huge prospect - one of those guys who comes along only once in a while.
"He has very high skill levels and is a big guy with it - he's quick and has all the power and explosiveness in his game that you can ask for.
There's a long way to go yet and there is a lot of ground for him to make up before he is the finished article but there is an inevitability about him getting there.
"There is one obvious comparison to make with Mike in his position and that's Terry Holmes. He is big aggressive, strong and very skillful."
Hansen also confirmed today that veteran Neil Jenkins would play his 100th and last game for Wales against the Barbarians at the Millennium Stadium on Saturday week.
Hansen, who names the rest of the squad next Wednesday, said: "The BaaBaas game is a great opportunity to send Neil off in an appropriate way.
"His body was telling him it was time to retire from international rugby, but we're pleased we can give him this last game at the Stadium in front of his fans," said Hansen, who confirmed Jenkins would start the match on the bench.
Jenkins said he was looking forward to the match.
"I think it's great of Steve and the guys in the squad to step aside and give me this opportunity," he said.
"I wouldn't have liked to end on 99 and a game at the Millennium Stadium is a perfect way to go out - I hope we get a good crowd for it."