As malphite, During this phase of the game, your only goal is to target the enemy backline and decimate them if you are going AP. Use the fog of war to do so.

If you happen to see someone careless enough to be sidelining alone, just go and kill them. This will allow you to get a numbers advantage and make a fight unfair.

Getting a defensive item like a Zhonya's should help you a lot with surviving your all-ins. It also bolsters your tankiness, so you may want to think about buying the item. As malphite, During this phase of the game, your only goal is to target the enemy backline and decimate them if you go AP. Use the fog of the war to do so. If you manage to see someone negligent enough to be sideline alone, just go and kill them. This will allow you to get an advantage of numbers and make an unfair fight.