def METHOD_NAME(stripped_phone_number: str):
    error_message = "Invalid phone number. Has to be a norwegian phone number"
    # https://www.nkom.no/telefoni-og-telefonnummer/telefonnummer-og-den-norske-nummerplan/alle-nummerserier-for-norske-telefonnumre#8_og_12sifrede_nummer
    if len(stripped_phone_number) != 8 and not stripped_phone_number.isdigit():
        raise GraphQLError(error_message)
    if not (stripped_phone_number.startswith("4") or stripped_phone_number.startswith("9")):
        raise GraphQLError(error_message)