Khao Lak is not in Phuket. It's 80kms north and is the resort area where 2000+ farangs died in the tsunami. It's about 1 hours drive once you've gone over the Sarasin bridge.
Khao Lak maps: map of Khao Lak
There's a lot of misleading advertising and listings done by hotels in Khao Lak. I've seen directories for supposedly hotels in Phuket which are actually in Khao Lak and they say (nearby Phuket). If you call 80kms nearby...then I'm a Dutchman!!!
There is very little nightlife there. It's mainly large resort complexes and attracts families; couples...and divers.