The Goddess Unleashed grants Fire Damage based on Physical Damage. x% of zero Physical Damage equals zero Fire Damage gained.

The wording is different than what I believe you thought, "(66-99)% ofAdded as Fire Damage"It is supposed to be based on the Sword's physical damage meaning it would add fire damage to non-physical spells but currently it is only acting as a "physical damage" modifier that is based on the physical damage of the spell rather than the sword.

The Goddess Unleashed grants Fire Damage based on Physical Damage. x% of zero Physical Damage equals zero Fire Damage gained.