Armor Malphite is the perfect match up for an AD heavy team and can be crucial in setting up the big team fights with his ult and the synergy he has with the size scaling on frost born gauntlets slow aoe. The most important thing for playing Malphite is to understand that you have such a low cool down on your ult and you don't need to hit the 5 man knock up. Your ult cd is so low you need to use it as much as possible even if it is just for one high value target. As armor Malphite you are a huge unstoppable rock barreling towards the enemy, start with your ult to hit your target(s) and use your E to reduce their attack speed, then pick a target that could get away and hit them with your q for the 40% slow. Finally as a side note because of the low cd on your ult you can use it to get away if you need to.

As full AP Malphite you are a heat seeking ballistic missile whose sole purpose is to blow up and act like you don't know no body. Your ult has full AP scaling and with max cd can get as low as 35.9 sec. Unlike armor Malphite you don't want to stick around after you ult, just try to full combo your target and use the speed boost on your q to run back to safety. As AP Malphite you act less like a support and more like an extra assassin, ganking lanes after 6 and bursting squishies. You don't have much health so don't confuse yourself with a front line tank, target the back line/caries and favor more of a hit and run style of play. One thing to note is that your q has a rally high cost so keep an eye on your mana and don't go in if your can't pull of your combos. Most important is to use your ult as much as possible, if you can get a kill and not die use your ult.