Man on phone fails to read a high risk of sucker punch or simply is unsure about how to respond to the risk.
The aggressor finally attempts a very poor sucker punch and the other man responds with a kick to the groin followed by punches which knock out the aggressor.
Something to note here is that unlike in the movies, the aggressor did not crumple to the ground once kicked in the groin, in fact he barely flinched at this. Closed fist punches to the head finished the fight which were set up by the groin kick.