Getting boots helps your mobility with malphite in beggining ganks or running away from one, also the mana pot helps your mana regen for more harass with seismic shard and the health pots just keep you up for your shield to regenerate. Sunfire cape is a good farmer item and a good 1v1 item with its damage per second. Even without mana you can 1v1 with normal attacks and ignite. Spirit Visage helps out with magic resist and a cooldown reduction. warmogs is a good health item for tanks in general. frozen mallet gives health and also allows u to gank by constantly slowing and finishing them off with ignite and sunfire cape without even using abilities if u have no mana. I dont think i have explain why thornmail and banshees veil are good. But i doubt you will even be able to buy frozen mallet without winning.

Flash is just a great help in general, you can flash to catch up for a seismic shard or a ground slam, even to get in rage for the ult. It also helps if your getting ganked. If your ult is up ur almost guaranteed a getaway by flashing through walls or ulting through one. Ignite is just good for a finish move if you think they're gonna get away with low health. Flashing in to ignite helps also.

21 in defense becasue in this build he is a tank i mean, 9 in attack because i like to actually be able to do some damage and not just be someone not to target first

This build is good for people who at least have some sense in playing malphite. I tend to win 10 out of 11 times if i have a descent team who doesnt feed. Thanks for looking. Also im bad with comps so if someone can comment how to post rescent games thatd be keww, Thanks