Not being familiar with the term PHlocking, I had to look it up. My Google research revealed that it’s related to Jimmy Buffett fans, whereby the Parrot Heads (PH) will phlock together at concerts and special fan club events related to their culture.
a1aparrotheads.org/ provides this description…
Parrot Heads will frequently add a “ph” to the beginning of words. This is an abbreviation of Parrot Head, which shortens references such as Parrot Head friends, Parrot Head flocking and Parrot Head festivities to phriends, phlocking, and phestivities.
Interesting to note that the phlocking term is being used for some Facebook events, which is where I first saw it.