How to hide the modal box after form submission using php?

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I have a page which return to the same page after form submission but it shows the modal box form , I want to hide the modal box when the user come page to the same page.
I had made the page using angular js and the website link is:
https://www.youstable.com/web-hosting-company-in-kanpur

2 
  <div class="modal" id="contactform" role="dialog" aria-labelledby="myModalLabel"
  aria-hidden="true">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header text-center">
          <h4 class="modal-title w-100 font-weight-bold">Fill Form And Start A Trial</h4>
<h5 class="modal-title">Call Us Now : +919616782253</h5>
      </div>
  <form name="userForm" method="post" action="contact.php">    <div class="modal-body mx-3">
        <div class="md-form mb-5">
          <i class="fa fa-user prefix"></i>
          <input type="text" name="inputName" id="inputName" class="form-control validate" placeholder="Your Name" required="">
        </div>

        <div class="md-form mb-5">
          <i class="fa fa-envelope prefix"></i>
          <input type="email" name="inputEmail" id="inputEmail" class="form-control validate" placeholder="Your Email" required="">
        </div>

        <div class="md-form mb-5">
          <i class="fa fa-phone prefix"></i>
          <input type="text" name="inputPhone" id="inputPhone" class="form-control validate" placeholder="Phone Number" required="">
        </div>

          <div class="md-form mb-5">
          <i class="fa fa-map-marker prefix"></i>
          <input type="text" name="city" class="form-control validate" placeholder="City" required="">
        </div>
          
        <div class="md-form">
          <i class="fa fa-pencil prefix"></i>
          <textarea type="text"  id="description" name="description" class="md-textarea  validate form-control" rows="3" placeholder="Write your requirement for web hosting" required=""></textarea>
        </div>

      </div>
      <div class="modal-footer d-flex justify-content-center">
        <button class="btn btn-unique" name="insert" type="Submit" value="Insert">Send <i class="fa fa-paper-plane-o ml-1"></i></button>
        </div>  </form>
    </div>
  </div>
</div>

<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<script type="text/javascript">
     setTimeout(function() {
    $('#contactform').modal();
}, 1500);
    
        $("#contactform").modal({
            backdrop: 'static',
            keyboard: false
        });
   
</script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
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