If it's the original Dark Phoenix Saga (by Chris Claremont & John Byrne) you are looking for, it contains Uncanny X-Men #129-136. But for the details you should go right back to issue 101 wherein Jean Grey was first believed to be possessed by the Phoenix.
And issue 137 is a fine story about how Cyclops looks back to their relationship and how he is dealing with the loss of his all-time lover.
It's an amazing series of events, with no equals in all the industry at that time. And it's a must-have for all and every single person who consider himself an X-Men-fan
Especially now that the movie is expected to be about the same happenings.
The Dark Phoenix Saga has been released in TPB for several times now, so it's really not too difficult to get it