You know how when shiki visited the Whitebeard Pirates Marco looked exactly the same? I think thats because his devil fruit gives him the power of a Phoenix he can be reborn and stay youthful forever. Mind blown
We're talking about the bird of legend that upon death becomes reborn in a LITERAL blaze of glory. Unless there are Buddhist in the series, which there aren't, They wouldn't have to pray to sengoku and even then thy would not because the devil fruit only gives you there abilities. It doesn't make you them.