Originally Posted by estnet
If you get the definite answer about UA please post as I may do this in the future.
I don't know about United but I was able to get my boarding pass to Phuket and stay in the international terminal when I arrived on Cathay Pacific.
The key is to check your luggage all the way through to Phuket . If you don't and only check it to Bangkok, you will have to clear immigration in Bangkok and re-check your bags over in the domestic terminal to Phuket.