Just got thorn last week, and will give you some tips. Stay in the hall right before going into the room where Phogoth is in. There will be some enemies that spawn here which willl eventually disappear, don't waste your ammo on them. Only kill the enemies which arrive from the hive ship. Make sure to take a fusion rifle for fire and arc damage. These will come in handy when destroying the wizards and knights shield. And lastly if it's a group of 3, don't go crazy on reviving teammates, they respawn after 30 secs. Take the mission slowly after 3rd or 4th ship, Xur will arrive and its a piece of cake. Good luck!