Enpi,
You can get good rates for smaller guesthouse and bungalow accomadation by booking in person, particularly when you are dealing with the owner, but I have always got better rates on the internet for larger hotels. Also, you are going to Phuket in "peak" season so a lot of hotels will be booked out at that time of year. If you are not fussy and you have time on your hands, you will find something, but I would book at least the first few nights.

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