First, it could be a huge mana ramp for the casting player , as you'll be able to attack the turn it comes into play and then tap all your land for double mana at the cost of that much damage
The exhaust ability is really strong
I also really like Caesar, Legions Emperors modal triggers, especially the card draw
The game plan is to build up massive beaters fast with your land triggers and deliver a wallop that nothing can withstand
And bouncing has a lot of flexibility as a way to survive removal or blocks, adding a useful tempo element, reloading a creature with a powerful enters-the-battlefield trigger, dealing with auras and so much more
Mono-Red Phoenix walks the line between quirky and competitive, and it could become a real player in the competitive scene in due time