IIRC the Phantom Mech ability is crazily powerful. It's not really balanced by anything else, so I don't know how you could even go about assigning it a point value. I don't believe it's ever been assigned a BV modifier, it should at least double a mech's BV, maybe even triple it. I don't think 2000xp would be too much, but then again I probably wouldn't want it at my game.
I think a better way to work it in would be if your character has a nemesis. The character and their nemesis both get the ability when they fight, but only from other units so they can have a grandiose duel in the middle of a pitched battle. It's still dramatic but it doesn't allow your character to dominate every other battle they are in.