<?php
 
$s = "he has a ferrari and ferrari 2 and what not.";
$replace = array  (
    "ferrari" => '<a href="x">ferrari</a>',
    "ferrari 2" => '<a href="x">ferrari 2</a>'
);
$keys = array_map('strlen', array_keys($replace));
array_multisort($keys, SORT_DESC, $replace);
 
$pat = '~' . implode("|", array_keys($replace)) . '~';
echo $pat . "\n";
 
$res = preg_replace_callback($pat, function($m) use ($replace) {
	   return isset($replace[$m[0]]) ? $replace[$m[0]] : $m[0]; 
	}, $s);
echo $res;

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