you could do the alternative such as
<script>
var guest = '<?php echo $guest; ?>';
$('.box').click(function(){ // labBox appears when box is clicked
if(guest === "true") {
$("#LabBox").hide();
} else {
$("#LabBox").show();
}
});
</script>
This would simply allow you to pass the PHP value to a Javascript variable, in order for you to use it within the onClick.