If you are looking for a place to party, this is not your island. In Phu Quoc I found only a couple of night bars. No discos, no clubs.
You will find the pubs on the road next to the tourist resorts. Ask your hotel If you do not find them. In the pubs, you can have a western dinner, drink a local beer while listening to pop music, play pool, and meet people from everywhere in the world. There is also a very active diving community. Remember this is an exclusive island. Do not expect big crowds.