star-thief is a cosmic being of untapped psychic potential. This is the first star thief i have never read any of the stories with the second or third characters so i don't know what they can do. I found a character bio here http://www.marvunapp.com/Appendix/starthf1.htm
the phoenix in this case is Jean grey as dark phoenix.
This battle is a race to see who can consume and or destroy the most stars in the galaxy, which is the ultimate goal.
Either party may choose to directly assault the other in an attempt to stop them from reaching there goal. Alternatively they could simply go directly towards the stars and simply destroy them
Phoenix can not go straight to the star-thiefs host and kill him.... that's no fun and doesn't make good battles
lets try and see who destroys what percentage of the milkyways galaxies first.