Phoenix without any avatar for me should be counted half as a wild animal half as a god with a morality so alien to ours that it is incomprehensible. That's why it needs hosts.
It is not like Galactus, with which one can reason in worldly terms. Phoenix caring for the mutants makes more sense with the conflict with the Dominions. Those AIs are anti-life, the death of the individual, a gray and metallic future. Mutation is change, adaptation, death and life.