public static function sanitize_phone(&$phone = '') {
		r_cast::string($phone, true);

		// Replace number chars.
		$from = \array_keys(constants::NUMBER_CHARS);
		$to = \array_values(constants::NUMBER_CHARS);
		$phone = \str_replace($from, $to, $phone);

		$phone = \preg_replace('/[^\d]/', '', $phone);

		if (! c_data::length_in_range($phone, static::MIN_LENGTH, static::MAX_LENGTH)) {
			$phone = false;
		}

		return true;
	}