If the sea is calm enough, you can have a chance to experience squid hunting. As most locals are fisherman, you can see how the process goes on. It must be really dark and no light is allowed so that you can catch the squid.
There isn't much nightlife on Phu Quoc. That's great really. Start your evening by watching the sun melt into the Pacific Ocean and then find a beachside spot for dinner. Rest your dinner down on the beach gazing up at the sea of stars, or across the sea at the galaxy of squid boat lights!