The hardest part is killing the phantoms. You can bring a hawk if you want because disarm works very good at this stage. Also when grimshaw is freed, run away to the locked door so he doesn't get scared and you are forced to kill all enemies (they don't shoot him). Also when he is unlocking the door you have time to get a laptop gun and deploy it on the bottom floor to help you when your fighting the phantoms (see 1:35 when I act crazy trying to find the gun).