You are welcome.
I am not sure exactly what kind of out-of-the-city experience you are looking for. Is it something like "in touch with nature simple living" or more like "tranquil luxury resort"?
I have never stayed overnight on Phi Phi myself. I have stayed on a liveaboard anchored in the bay though. I believe there are a couple of luxury resorts on Phi Phi on secluded beaches only reachable by boat. Those are probably tranquil and quiet. The most developed area in the center of Phi Phi explodes in loud beach parties and fire shows for backpackers in their twenties drinking from buckets every night. Quite entertaining but maybe not what you are looking for. The famous Maya bay featured in the movie the beach gets so may tourists every day that you can hardly see the sand. The scenery around Phi Phi is extremely beautiful but also very crowded.
The diving around Phi Phi is great. You can reach most of the same dive sites from Phuket, Ao Nang, or Koh Lanta, but Phi Phi is generally closer. Koh Lanta is closer to Hin Daeng, Hin Muang and Koh Haa, but those sites are closed at that time of year.
Google maps of Koh Phi Phi:
https://www.google.dk/maps/place/Ph...:0xbf9db8781a549f71!8m2!3d7.740738!4d98.77841