Phuket is a big island with a lot to explore including its historical heritage, temples, beaches, places. waterfalls, pristine beaches, islands around it etc. I’ve been living in Phuket for many years and still find a lot of new things (temples, roads, places, beaches) but if you just go with the crowd and follow regular tourist routes you’ll never see it. But that’s another story
It’s pretty much same rainy everywhere in Thailand in this time of the year. Choose a place when you can still explore a lot even if it rains, for example Phuket