Shopping centres such as Central Festival, Big C, Lotus, Robinson and Ocean Plaza are on the way to Phuket city or in Phuket city and are open 10:00-22:00. These are good places to hang out if you are tired of the beach and the sun. And why not finish the shopping day with a good movie in one of the theatres at Central Festival or Ocean Plaza. The prices are between 80-120B.
Restaurants, well Phuket is a tourist island and you will find all kinds of food from all over the world, but don't forget to eat the local cuisine and feel the hot/spicy chilli taste while cooling it down with a locally brewed beer. Another recommendation is the seafood, this is the right place for good cheap seafood.
Spa and Massage in the city are more professional and little bit cheaper than the ones at the tourist areas, but don't expect a fluent English masseuse.
Fun for the kids, Phuket Zoo located south of Phuket city on the way to Chalong bay and Phuket Aquarium at Ao Mahkan bay.
Fun for the big ones, not so much to say here. There are lot of bars, karaoke, night clubs and discos in town. Some of the popular ones are Jammin, Thimber Hut, Ozone and Kor Tor Mor. Long pants are recommended for two reasons, mosquitos and some of those places wont let you in with shorts.