Phantom Riding Glitch

The Phantom Riding Glitch is a glitch can be performed in the Campaigns of both Halo 2 and Halo 3. It allows the player to travel within a Phantom. However, the player will invariably die, either by falling off or when the Phantom flies into a kill barrier.

Outskirts
Riding a Phantom is easy in Outskirts. You should have the Sputnik Skull activated. Simply:
 * 1) Drive a Ghost through the level until you get to the beginning of the tunnel.
 * 2) Kill all enemies and allies,.
 * 3) Shoot the Phantom's turrets off with a Rocket Launcher.
 * 4) It will look at you, and follow you if you move.
 * 5) Jump onto the top of the tunnel; to do that simply Explosive Jump up, or jump on top of a Warthog, then jump up.
 * 6) Jump on top of the Phantom, and it will eventually fly away, taking you with it.

Metropolis
You can also do this on Metropolis. To ride a Phantom on the bridge, do what is shown in this video. 

You can also ride on a Phantom by hijacking a Banshee and doing the same procedure that you would do to get the Scarab Gun.
 * 1) Do the Banshee glitch.
 * 2) Jump on top of a Phantom.

Quarantine Zone
It is possible to ride the Phantom that follows you in Quarantine Zone. To do this, have the Sputnik Skull activated. When you get onto the elevator, go to the back and quickly grenade jump. If you land correctly, you will stay on the Phantom. However, after a while, the Phantom will speed up and you will fall to your death.

Sierra 117
At the chapter Quid Pro Quo in Sierra 117, you can get onto the roof of the building where Sergeant Johnson is being held; there should be a Phantom dropping off Covenant forces. From that position, kill the Grunt manning the Plasma Cannon, and jump towards the turret while holding RB. Now press RB again and jump backwards. You should now be inside of the Phantom.

Crow's Nest
In Crow's Nest, when you reach the hangar, there will be little metal arches that can be jumped onto. Jump onto the very first one to the left and wait for the Phantom to enter. When it gets nearby, hold RB and jump towards the side-mounted Plasma Cannon to grab it. Now press RB again and jump backwards. You should now be inside of the Phantom.

When the Phantom leaves, you will be thrown to the back. Hold forward and you should be able to move. After that, quickly get back on the turret. The Phantom will fly for a little bit until it eventually drops. After that, you can flip it with RB and use it like a catapult.

There is another way to get in, however. When you enter the hangar, grab one of the Deployable Covers near the door. Get on one of the metal arches, then face down. Drop the Deployable Cover, and at the same time, jump, so that you land on it when it activates. When the Phantom docks, jump off the shield and into the Phantom. This way is easier than the first, because you won't have to risk falling through the Phantom when you dismount the Plasma Cannon. However, you still need to mount the Plasma Cannons when the Phantom is outside of the hangar.

The Covenant
After deactivating third tower on The Covenant, quickly run along the right side towards the green Covenant Separatist Phantom, kill the Elite on the turret, and then grab it with RB. Stay on the turret. The Phantom will engage Active Camo, and after this point, it will be deleted when you let go of the turret.

It is also possible to remain on the Phantom after it engages Active Camo by attempting to walk into the Gravity Lift. When the camouflage engages, you will glitch into a rider position. You will continue to ride until the Phantom reaches the edge of the map, then you will sink at a constant rate (not fall) until you enter the water and die.

Trivia

 * You're also able to take a Phantom ride out of the map Tsavo Highway.
 * In Theater, in Crow's Nest, you can travel towards the Covenant ship in the distance. You'll find that the other half of the ship is missing.
 * You have the ability to flip the Phantom once it crashes near the rocks. This is similar to riding the pelican in the Halo 2 level Metropolis. Once it lands, you can flip it by pressing X.