Around the time of the full moon every month - many of the backpackers and party goers head for Koh Phangan for the full moon parties, leaving Phi Phi relatively empty.
Making it the perfect time to visit Phi Phi for those who prefer a more peaceful relaxing time, and to get the beach to themselves.
So if you want to avoid the hustle and bustle, talk to the locals or see the surrounding islands when they are less busy, then why not come to Phi Phi during the full moon period.