Phuket's warm Andaman waters are home to a selection of popular dive destinations. The aptly named anemone reef is also home to lion fish and leopard sharks whilst moray eels and gorgonians reside a little further offshore at Koh Dok Mai.
There is also an artificial reef created by wrecked ferry vessel King Cruiser which creates a busy home for many fish. A great array of fish including manta rays and whale sharks are spotted at the close by Racha Noi and Racha Yai islands. Shore diving and snorkelling is also popular around Phuket.
Here's a great Phuket Blog that also covers other places in Thailand.