Phillips, the 22-year-old Wales' international, is currently with Llanelli Scarlets and will transfer to the Blues at the end of the current season. He won his fourth cap against Japan last November.
Cardiff Blues' chief executive Robert Norster said, "These are another two important contractual agreements for our regional squad as we continue to plan the way forward for next season and beyond. All teams require strong selection options and competition for places, especially when injury takes a hand as it has in such pivotal positions for us this season. We have been particularly unfortunate at scrum-half. Now Ryan is back to full fitness and with Mike coming on board we have just that. They are two outstanding players and our future prospects can only be enhanced by their presence. With Robert Howley also joining us as backs' coach the two of them will particularly benefit from his expertise."