Flank and assist offensive pushes or weaking the enemy pushes for your teams defense.
Sneak and kill problematic Vassilis to allow your team to push forward.
Flank and harass the side objectives.
Kill Medics
Perform objectives if possible
Guard C4
Guard your disarmers. I often turn on refractive armor and meat shield the people disarming if they’re under fire
Revive people when you can.
All of these things you should be flanking or taking alternate routes, sometimes you can get away stealthing and sprinting through cross fire, but I typically do that to kill people repairing EVs or planting/disarming C4.
Many more options, but you should be flanking, striking hard and fast. Distracting is very easy as a phantom. People are so terrified, you can lead them off objectives. I had a game tonight where we were defending on chapel, and I was running to the spawn so I could switch over to the side with the bridge generator. A wave spawned as I was passing through, I ended up long jumping and running towards previous objectives and managed to get 4 people chasing me instead of escorting the data cores.