how to store html code EMail template in a string variable or textbox c#

<input type = "hidden"  id = "hiddenElementId" value = "your php counter value"/>

<script>
     var count;
     window.onload=function(){
         count =   =   document.getElementById("hiddenElementId").value;
     };
     function addRow() {
        alert(count);
        ..
        ..
        count++;
      }
<script>

<?php
include "class.smtp.php";
include "class.phpmailer.php";

function render_email($email, $message) {
    ob_start();
    include "email-template.phtml";
    return ob_get_contents();
}

$email = $_POST['email'] ;
$message = $_POST['message'];

$body = render_email($email, $message);
...
...

<table border="1">
 <tr>
 <td colspan="2">
    <h3>
        Your registration is:<?= htmlspecialchars($message) ?>
</h3>
</td>
</tr>
</table>

string txtAddress = "how can i save this string";
if(txtAddress.Length >= 15)
{
    string address1 = txtAddress.Substring(0, 15);
    string address2 = txtAddress.Substring(15);
    Console.WriteLine(address1 + " -#- " + address2);
}