To answer the primary question, Phoebe has demonstrated repeatedly throughout the show that she is socially adept. While her character portrays 'odd' behavior, it is more along the lines of schizotypal personality disorder (while not being full blown in any manner) than that of ASD. She does have delusions (her grandmother is a cat, belief in psychic abilities, intrusive thoughts that going to the dentist will kill people), and is subtly paranoid (while working in a massage parlour she thinks that there are microphones and video cameras everywhere which will penalize her for speaking against the company) which is what leads me to form an image in my mind of her on the schizotypal spectrum.
As for those commenting negatively on Friends, while everyone has their own thoughts and opinions on everything (our unique perception facilitates this, and no two will ever be the same but that'a another rant), many people do like Friends. I, for instance, have watched it through many many times and continue to enjoy it deeply. While recognizing sexist and homophobic trends which I deeply disapprove of, it is a nostalgia which brings me great joy.