Phero is literally an inferior MBeedrill. It lacks Adaptability and has worse overall bulk. MBeedrill can actually kill Ghosts due to having Knock Off as well as have an easier time killing Toxapex due to having Drill Run. As if that wasn't enough, it can finish off a weakened enemy or OHKO a frail one like Greninja with Fell Stinger to get a massive Attack boost while Pheromosa would have to knock out half the opponent's team to get that same boost. MBeedrill is flat out better and Pheromosa a shit.