Since Paul lived and worked in the greater Syrian area as a Pharisee, it is somewhat probable that Pharisaism had some influence there and that some Pharisees lived outside Jerusalem and Judea. […] Paul never says where he made contact with Pharisaism, in Tarsus, Syria, or Jerusalem. […] The evidence concerning Pharisaism is so slim that we do not know how Paul came to know about Pharisaism, why he was attracted to it, and what being a Pharisee entailed.
Source: wiktionary