If we’re going to be dealing with souls, it might be a good tie-in with either Hades or Ursula.
That being said, I don’t think Phillip is dead. His soul is merely trapped in the medallion therein, instigating/assuring that he will remain asleep ( much like Aurora was ) until his soul can be returned to him.
That also means someone needs to find a way to release his soul & you have to wonder if each wraith has their own medallion or if that one medallion contains many other souls.