Phuket has a great variety of beaches.  From jam-packed with tourists right in front of Patong Beach - to near deserted beaches on the northern part of the island - to hidden away beaches like Laem Singh.  Get out and see the variety available at Phuket's Best Beaches . 

Naithon and Layan Beaches are far less crowded than the tourist havens to the south.  If you seek a quiet, yet very lovely beach, those two are excellent places to start.  

See Freedom Beach.  Take a long tailed boat from Patong and you will see one of the best and most secluded beaches.