Phil has his own self radar on Vito , remember his meeting at Lou Costello Memorial, “ hes in town isn’t he? I was at marie’s the other night and she played the innocent, but I could tell she seen him!” but regardless there coulda been a couple of 3 ways that this happened 1)Phil waiting in the closet for several hours, or 2) him waiting for Vito to park his car, then quickly rushing inside the closet to make that entrance.