If:
the PHP script is marked executable
AND
the first line is a #! line with the path to your PHP binary.
otherwise, you'd be better off specifying the path to the PHP binary and the name of the script on the command line itself.
Code:
#!/bin/bash
PHP=/usr/local/bin/php
$PHP /usr/etc/script.php
Check the man page for any switches you might need to add (depending on the script).