Well, he went to one of the old Goblin hideouts he used to go because he wanted to impress Norah Winters with some stuff there. Roderick Kingsley had just returned as the Hobgoblin and was checking this same place out at the same time, he found Phil was there and was going to kill him but Phil used the lunatic laugh on him to paralyse him. Then he chopped his head off with a flaming sword, one of the new weapons Osborn had made.
So he seemingly killed Kingsley, I can imagine another writer down the line will try to retcon that but Phil is awesome as the Hobgoblin right now.