- preg_replace: documentation ( source)
<?php
$re = '/(")([^"]+)(")/';
$str = 'The nice man said "How\'s things today" and I replied "All is good thanks".';
$subst = '<i class="fa fa-quote-left" aria-hidden="true"></i>\\2<i class="fa fa-quote-right" aria-hidden="true"></i>';
echo preg_replace($re, $subst, $str);