I think you would need to go to Krabi to reach Phi Phi Islands, bit far for longboats. You should then be able to get another boat to Phuket. Why not go to Phuket and take a trip from there to Phi Phi? I believe Phuket and Krabi are equidistance to Phi Phi.

Since the tsunami things have changed a lot at Phi Phi. Worth trying the Lonely Planet thorntree forum for uptodate information.