<?php

$haystack = <<<DOC
Lorem ipsum -[blank]- sit amet, consectetur
adipiscing elit. Donec condimentum augue 
sit amet blandit vehicula. Nullam placerat
aliquam dictum. Quisque elementum nisl
sed pellentesque elementum. Aliquam erat
volutpat. Suspendisse potenti. Maecenas [blank].
DOC;
 
$array = ['cat', 'mole'];
$needle = '[blank]';
 
foreach($array as $replacement) {
	$pos = strpos($haystack, $needle);
	if ($pos !== false) {
		$haystack = substr_replace($haystack, $replacement, $pos, strlen($needle));
	}
}
 
echo $haystack;