Siam has to be one of my favourite Thai restaurants outside of Thailand, worldwide.
Having spent three months in Thailand I became a big fan of going from place to place sampling the various different takes on certain dishes. Siam provides the taste that takes me back to the great times I spent out there in providing authentic food with deep flavours with all the right ingredients.
The staff are incredibly friendly and always happy to help.
The food comes in large, family sized portions. This is especially effective with the soups (I thoroughly recommend the Tom Yum) that are presented in a Thai Fire Pot. Great for get togethers, just take the ladle and dish it out.
The only draw back to this is that if you are ordering for one or two people, it doesn't give you great scope to try a variety of foods (unless you want to go home with LOTS of left overs... actually no, that's a great idea!).
All in all, every return to Phoenix just isn't complete without a trip to Siam. Go try it, you won't be disappointed!