Why not make Phantom completely invisible if he's crouching 5m near a friendly deployable, and make his EMP an actual grenade? We can buff Bushwhacker this way, and Aura would stay the same because Rhino's a better choice on a health station.
We could still use the shimmering texture Phantom has when he uses a weapon, which lasts for twice the amount of time that said weapon's fire delay would be, but scales appropriately.
I know that this seems like a weird rework (making something that doesn't alter base stats a passive/triggered ability) but I think this could work. It makes him able to switch in and out of cloak quick enough to be dangerous as a defensive class, and gives him an offensive ability.