PHOENIX — The last serious sighting of Cain Velasquez came 30 months ago, when the former two-time heavyweight champion stopped by the UFC’s bicentennial show to remind the fight game of his terrifying brilliance by ripping apart Travis Browne as if tasked with the easiest job in the world. It was short. It was violent. It was vintage. He melted back into the heavyweight ether after that, as he is wont to do, a ghost who reanimates himself every so often just to prod the UFC’s big boys with the knowledge that their house is still haunted by an infrequent force beyond their control.