Before. There's desks right next to the transit security entrance, although it seems like PAL's is in T1.

That said, Delta should arrive into T2 and Philippine Airlines operates out of T1 at TPE. There's no train airside so it's going to quite a walk, TPE website is showing arrival into D9 which is literally one of the furthest gates from T1.

You'd probably be best to just ask the ground staff guiding people towards immigration/transfer where to go. Not sure if they'll let you walk from T1 to T2 before going through transit security or send you through T2 transit security without a BP

Good luck!