FRIDGE is spelled phonetically so that upon encountering it in print you’ll know how to pronounce it. At the time, it was a new coinage (hell, it’s still less than a century old) and at the time they were focused on spelling by rule instead of by rote.
Nazi Officer: “Sir, we are mining too many useless ores”
Hitler rubs chin: “So mine less”
Grammar Nazi busts in: “MINE FEWER”
Hitler looks up: "Yes?”