Parses the given phone, or returns ``None`` if it's invalid.

def parse_phone(phone):
    """Parses the given phone, or returns ``None`` if it's invalid."""
    if isinstance(phone, int):
        return str(phone)
    else:
        phone = re.sub(r'[+()\s-]', '', str(phone))
        if phone.isdigit():
            return phone