(PHP) Why is this while loop an infinite loop?

Can you please help me understand why this while loop repeats at 1 infinitely? What I'm trying to do it make a function that calls itself and prints out every number that is passed into is via the parameter.

<?php
function least($num) { echo $num . '<br>'; $num -= 1; while ($num > 0) { least($num); }
}
echo least(10);
?>