Uncanny X-Men #135 is a key part in the Dark Phoenix Saga. Basically Phoenix goes completely nuts, killing off all the nice people in the picture above. So why do we care so much?
By this point it becomes perfectly clear to the rest of the X-Men that Jean Grey is gone and that the Phoenix Force has completely taken over her physical form. Unfortunately, there isn’t much left that they can do to stop her, short of killing her.