Can take teleport instead of ghost.
Start with cloth armor and 5 pots.
Start on blue and work across towards the golems.
Malphite needs the blue buff to jungle effectively at the beginning. Make sure that your teammates are willing to support you because you are vulnerable to ganks at this point in time. Once you get rolling, you can jungle very fast and can continue to jungle between team fights for the entire game.
The build above is actually focused more on ganking and not jungleing. If, for some absurd reason, you want to jungle more/faster and gank less/less effectively then get the madred's razors before the boots and skill up ground slam before seismic shard. However, be warned, malphite is a VERY good ganker and you will be serving your team more by ganking early then by farming up for the late game.
Try to only drink 3 pots on the first trip and save the other 2 for the second trip.
Gank a lot. Your passive makes it cost very little health to exchange blows a bit.
Buy Ninja Tabi after first back.
If the other team lacks a jungler, you can use your 2 leftover pots to jungle their side on your first trip out. Then, by the time you back, your blue should be coming up again. If you get in two full "whole jungle" runs before any major setbacks, you will be able to carry the game. Even when jungling in this way, be sure to gank each lane as you approach it.
Learn to be constantly jungling near the action. You need to be close enough to be a part of all team fights, but also, you need to farming and leveling in the jungle. By mid game, you can clear the small camps so fast that you barely even slow down your movement. It is ok as Malphite if you are a second or two late to the party, but you can't be more late than that, or you will miss the party altogether, and most likely you will be partying alone because all your friends died in your absence.
Malphite builds like a tank but plays like an assassin. Your ult is a very good initiation and you will have the survivability to jump in and give the other team a beating without getting melted. However, I much prefer if a full tank then follows me in and allows me to run out again while my cooldowns are coming back up.
When you decide to initiate, turn on your W, then R into as many people as you can. While they are still in the air, hit E. When they land, look for someone who is low, or someone who is a priority target and then Q that person. Now get out. When Q and E come back up, get back in there and get as many people as you can with E. Alternatively, you can initiate as above and then also be the cleanup chaser. Just pick a target and follow them while you are waiting on Q and E to come back up.
If the other team initiates on you, defend your squishies. R+E whoever is on your squishies and then Q them while the squishies run away. Often you can turn the situation around so much that the squishes can stop running and start racking up kills. Remember that you are not a full tank and need to back alongside the squishes. You can create an opportunity for them to get to safety, but you need to be looking for a way out yourself. Do not hesitate to use R as an escape. It will be back up faster than you would be if you died.
If the game goes long, you are farming well, or you are getting a lot of kills (best option; get out there and gank), then you will likely need to purchase some additional items. The rest of the items are situational so we will look a t a few that are likely to be good investments.
Force of Nature - I build this item next most games. The core build lacks magic resist and this is the magic resist item for me. You could build a banshee's Veil I guess but the Force of Nature is much tankier and honestly, Malphite is himself a force of nature.
Randuin's Omen - If the other team lacks Magic DPS, then skip the Force of Nature and get this. Randuin's is just pro on Malphite. I have considered replacing the Frozen heart with this, but I have mana problems. Also with both, you are at max cooldown reduction, which I absolutely love with every champ in the game. If you know in the loading screen that the other team is not going to have any Magic DPS, then I would actually build the Heart of Gold half of this first and then build boots and the rest of the core items while the HoG is making money. Don't forget that this item has an active. Make it a part of your initiation combo.
Frozen Mallet - Just a great item. The core build could use more heath and this provides it. With your Q and the slow from Frozen Mallet, very few champions will be able to run from you. This also makes you a better squshiesitter.
Inifinity Edge - Team lacks damage? ROFLstomping the other team? IE is your answer. I hardly ever get this, be some strange situations seem to call for it.
One more note - Keep the Wriggle's Lantern ward on cooldown. I use it for constant dragon warding.
Have fun and gank more. If your game doesn't seem to be working right, you are not ganking enough. I sometimes gank a lane, then clear one small jungle camp, then gank that same lane again. Gank, Gank, Gank.