How to add T in date in php code example

Example 1: php date plus days

<?php 
// PHP program to add days to $Date 
  
// Declare a date 
$date = "2019-05-10"; 
  
// Add days to date and display it 
echo date('Y-m-d', strtotime($date. ' + 10 days')); 
  
?>

Example 2: add 6 months to date in php

$effectiveDate = date('Y-m-d', strtotime("+3 months", strtotime($effectiveDate)));