Using a script as the command name only works if the script begins with a
shebang line pointing to the command line php interpreter (e.g. /usr/local/bin/php) and the script has executable
permissions (mode 750). However, scripts don't process QUERY_STRING when run from the command line, so you won't be able to use $_GET or $_POST, or any other magic globals, such as $_SERVER, so the shebang line and permissions are a dead end.
You've got two options: use wget (or curl) to fetch the URL or pass the arguments on the command line and read them from
$argv in the script. If you need to be able to access the script as a page via the web, use the former method. Otherwise, use the latter, which is less resource intensive.
For more information, read: "
Cron Jobs", "
Crons don't work", and "
Cron Question".