JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.13.1/jquery.validate.min.js"></script>
<script src="https://img.infocert.it/js/libphonenumber.js"></script>
<script src="https://img.infocert.it/js/intlTelInput.min.js"></script>
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<fieldset id="richiedi">
    <form action="" method="POST" name="WebToLeadForm" method="POST" id="WebToLeadForm" class="form-horizontal col-md-11">
        <input type="hidden" name="oid">
        <p>&nbsp;</p>
        <p><b>Per essere contattato da un commerciale</b>, compila il form sottostante. I campi richiesti sono obbligatori.
            <br />
        </p>
        <div class="form-group">
            <label class="col-md-3 control-label" for="first_name">Nome:</label>
            <div class="col-md-9">
                <input class="form-control" id="first_name" name="first_name" maxlength="40" tabindex="1" type="text"> <span class="glyphicons form-control-feedback" aria-hidden="true"></span>

            </div>
        </div>
        <div class="form-group">
            <label class="col-md-3 control-label" for="last_name">Cognome:</label>
            <div class="col-md-9">
                <input class="form-control" id="last_name" name="last_name" maxlength="80" tabindex="2" type="text">	<span class="glyphicons form-control-feedback"></span>

            </div>
        </div>
        <div class="form-group">
            <label class="col-md-3 control-label" for="company">Azienda:</label>
            <div class="col-md-9">
                <input class="form-control" id="company" name="company" maxlength="40" tabindex="3" type="text">	<span class="glyphicons form-control-feedback" aria-hidden="true"></span>

            </div>
        </div>
        <input type="hidden" name="city" value="">
        <div class="form-group">
          ...

JavaScript

$(document).ready(function () {

     $("#phone").intlTelInput({
         //allowExtensions: true,
         //autoFormat: false,
         //autoHideDialCode: false,
         autoPlaceholder: false,
         defaultCountry: "it",
         //ipinfoToken: "yolo",
         //nationalMode: false,
         //numberType: "MOBILE",
         //onlyCountries: ['us', 'gb', 'ch', 'ca', 'do'],
         preferredCountries: ['it'],
         utilsScript: "https://img.infocert.it/js/libphonenumber.js"
     });

     var telInput = $("#phone"),
         errorMsg = $("#error-msg"),
         validMsg = $("#valid-msg");

     // on blur: validate
     telInput.focusout(function () {
         if ($.trim(telInput.val())) {
             if (telInput.intlTelInput("isValidNumber")) {
                 validMsg.removeClass("hide");
             } else {
                 telInput.addClass("error");
                 errorMsg.removeClass("hide");
                 validMsg.addClass("hide");
             }
         }
         var numberType = $("#phone").intlTelInput("getNumberType");
         if (numberType == intlTelInputUtils.numberType.MOBILE) {
             // is a mobile number
             $("#phone").attr('name', 'mobile');
         } else {
             $("#phone").attr('name', 'phone');
         }
     });

     // on keydown: reset
     telInput.keydown(function () {
         telInput.removeClass("error");
         errorMsg.addClass("hide");
         validMsg.addClass("hide");
     });
     $("#text_message").focusout(function () {
         $("#00Nw00000088clXEAQ").val($("#text_message").val())
     })

     jQuery.validator.addMethod('validatePhone', function () {
         if ($("#phone").intlTelInput("isValidNumber")) {
             return true;
         } else {
             return false;
         }
     }, "Numero non valido");


     $("#WebToLeadForm").validate({
         errorElement: 'small',
         errorClass: 'help-block',
         errorPlacement: function (error, element)...