they all have the same abilities except their morphing abilties are different:
the morphing ability is based off of Phoenix Morphing (Egg Related):
Morphing ability level 1: Normal Unit Form: Phoenix level 1 - Alternate Form: Egg level 1
Morphing ability level 2: Normal Unit Form: Phoenix level 2 - Alternate Form: Egg level 2
Morphing ability level 3: Normal Unit Form: Phoenix level 3 - Alternate Form: Egg level 3
the only difference between phoenix level 1 and 2 and 3 are their stats. Eggs have different stats in different levels as well. and the phoenixes have their morphing abilities (phoenix level 1 has morphing ability level 1 etc etc)
now for the bug:
you summon the phoenix
the phoenix has negative hp regeneration so its health will run out.
once the health ran out, it should become an egg but no, after morphed, you can move the phoenix, it can attack (although the egg timer starts to run out) and it has no model.