Easily removable, for sure, but how many times? I think it could have a lower health, like 4, and the cost of rebirth should be 2 at least.
Perhaps leave it as it is, but increase the cost of rebirth to 2
. While it has high health, you must understand that it cannot do damage unless it is reborn. In many cases, you can simply devour the Phoenix and leave the Ashes be until they reborn. It is more food for your Oty and over time, effectively halves the damage of a Phoenix (4 damage over 2 turns).
I think it is fine as it is without changing the cost of rebirth, but might need some tweaking as the full extent of its effectiveness is still not yet established.