JSFiddle - React, Tailwind, and code Playground

HTML

<input id="filterconfphone" type="checkbox" onchange="filterconfphone_click()">

JavaScript

function filterconfphone_click() {
  alert (document.getElementById('filterconfphone').checked);
  //var checkbox = document.getElementById('filterconfphone');
  //if (checkbox.checked != true)
  //{
  //  alert(checkbox.checked);
  //}
}