protected function phone($key) : bool
    {
        $num = preg_replace('/d+/', '', (int) $this->param[$key]);

        $conCate = '';
        $columnName = ucfirst($this->convertToFieldName($key)).' should be ';
        if (isset($this->errors[$key.self::ERROR])) {
            $conCate = str_replace('.', '', $this->errors[$key.self::ERROR]).' and ';
            $columnName = '';
        }

        if (in_array(strlen($num), $this->validPhoneNumbers) == false) {
            $this->errors[$key.self::ERROR] = $conCate.$columnName.'valid phone number.';

            return false;
        }

        return true;
    }