I'm 5'8" 165 and even I find boards 51" and up too large (when it comes to skimboards). You are smaller than most wakesurfers, and you will appreciate riding a board that is the proper size. Wakesurf boards cost a lot of money, and it would suck to spend that money on something that doesnt work for you like it should.
Again, if you are set on a phase 5, the Diamond Luv is a great shape and will work better than the 51 regular diamond.
Luckily more companies are starting to make smaller boards. Not everyone is 6 foot tall and 200 lbs