No. Phil Mickelson is not a member of the Church of Jesus Christ of Latter-day Saints (also called the "Mormon" church). He and his wife have been very quiet about their religious beliefs.
He uses an Odyssey XG9 PM (Phil Mickelson) Prototype which he helped design. You can't buy a replica of his, but you can buy the XG9 which is very similar, just a different colour, the retail ones...