<?php
$patterns = ["re", "get", "ER"];
$string = "You are definitely getting better today";
$alternations = implode('|', $patterns);
$re = '(?!(?<=\s)(?:'.$alternations.')(?=\s))\S*(?:'.$alternations.')\S*';
$string = preg_replace('#'.$re.'#', '', $string);
$string = preg_replace('#\h{2,}#', ' ', $string);
echo $string;