Hi Maxcat welcome to the forum.
Check out CathyP's website for heaps of ideas
http://cathyandgarystravelpages.com/phuket.htmI would highly recommend I did a day trip last a day trip with Phuket Sail Tour, you will find a a review and link to them on Cathys site.
Last year we did a day trip with a private driver, Daj, who is also listed on Cathy's site. This was a greatday out, you are in control of what, where and how long you spend at places cause its your day trip. It cost us about $100Aus for the day (its a mini bus so up to eight people can go for that price). The only other cost are the activities you choose to do, eg elephant riding. It was fab, Daj has some options set out but you can add or change what you want. The trip we did was from Patong south down the coast to the lookouts and beaches, this can include elephants at Kok Chang. From here we choose to go to an orchid farm (my friend is orchid mad!!) or you could go to the aquarium etc. We then went to Wat Chalong, then off to a waterfall and Gibbon rehabilition centre.
Cheers
Michelle