Everyone here is trying to explain how a Phoenix commits suicide in burning fires to become reborn.
...
Flying in the air and crashing down as a fireball makes perfect sense for you to receive damage.
I'm a bit confused why people keep insisting this is supposed to be "just like a phoenix" right up until that whole reborn part of a phoenix's life. I don't consider
"arriving very damaged and in a burning state that will bring you to death" reminiscent of the phoenix's ability to be reborn anew.
Maybe it should have been called
"Almost a Phoenix Dive, But More Like a Flaming Swan"?
Or we could just fix the whole set-the-user-on-fire bit, since this is a Warrior skill and not pyro-mage spell. (Fun fact: at one point Phoenix Dive was a mage spell.)