Hence why you can have 50 people solo the rancor (500+ million damage to a 10.3 million health pool). Each person's damage counts towards the phase total, and everyone's individual scores are displayed in the list.
Like the above said, when phases are close to ending people need to be communicating or watching the Guild chat for instructions. That's the only point you want to go in one-by-one otherwise that team is unable to be used again when they could actually score full damage.