def METHOD_NAME(phone_hash: str) -> None:
    """Remove a phone number if it has no inbound references."""
    phone_number = PhoneNumber.get(phone_hash=phone_hash)
    if phone_number is not None and phone_number.refcount() == 0:
        app.logger.info("Forgetting phone number with hash %s", phone_hash)
        phone_number.mark_forgotten()
        db.session.commit()
        statsd.incr('phone_number.forgotten')