Where to stay in Phuket and other destinations?

After 4 nights in Bangkok and 6 days in Perth I'm flying to Phuket. I'll have about 10 days then to chill. I would like to stay in Krabi, Railey and visit Phi Phi etc. Does anyone have any advice where to stay.

Should I book all rooms before I go or just turn up? Will be early january when I arrive.
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