twilio-sheet/webapp/Page.html

<!DOCTYPE html>
<html>
  <h1>Let's send you a text</h1>
  <p>Please enter your phone number without any special characters or spaces.</p>
  <label>Phone number: </label><input type="text" id="phoneInput" placeholder="ex: 9990001234">
  <button id="submitButton">Submit</button>

  <script>
  document.getElementById('submitButton').addEventListener('click', function() {
    // Get the value from the `phoneInput` text box.
    var phoneNumber = document.getElementById('phoneInput').value;
    
    // Run the Apps Script `userClicked` function passing the `phoneNumber` input.
    google.script.run.userClicked(phoneNumber);
    
    // Clear the `phoneInput` text box.
    document.getElementById('phoneInput').value = '';
  });
  </script>
</html>