Pass PHP variable to bootstrap modal

put this inside your loop

<button type="button" class="btn btn-success" data-toggle="modal" data-target="#message<?php echo $row['id'];?>">Message</button>

<div id="message<?php echo $row['id'];?>" class="modal fade" role="dialog">
  <div class="modal-dialog">

    <!-- Modal content-->
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal">&times;</button>
        <h4 class="modal-title">Modal Header</h4>
      </div>
      <div class="modal-body">
        <p>Some text in the modal.</p>
        <?php echo $row['id'];?>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
      </div>
    </div>

  </div>
</div>

If, I got you correct.

The modal trigger button with $row['ID']

$order .= '<td><a href="#myModal" class="btn btn-default btn-small" id="custId" data-toggle="modal" data-id="'.$row['ID'].'">Edit</a></td>';

Bootstrap Modal event to fetch the $row['ID'] value with Ajax method

$(document).ready(function(){
    $('#myModal').on('show.bs.modal', function (e) {
        var rowid = $(e.relatedTarget).data('id');
        $.ajax({
            type : 'post',
            url : 'fetch_record.php', //Here you will fetch records 
            data :  'rowid='+ rowid, //Pass $id
            success : function(data){
            $('.fetched-data').html(data);//Show fetched data from database
            }
        });
     });
});

Modal HTML

<div class="modal fade" id="myModal" role="dialog">
    <div class="modal-dialog" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal">&times;</button>
                <h4 class="modal-title">Edit Data</h4>
            </div>
            <div class="modal-body">
                <div class="fetched-data"></div> //Here Will show the Data
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

Last Create fetch_record.php, retrieve the record and show in modal

<?php
//Include database connection
if($_POST['rowid']) {
    $id = $_POST['rowid']; //escape string
    // Run the Query
    // Fetch Records
    // Echo the data you want to show in modal
 }
?>