There are two ways of running a PHP script locally.
One is to have cron start a web client, pass it the name of the php script as a command-line argument, have the client request the script from the web server, and throw away the result the response from the web server.
The other is to have cron start the PHP executable, pass it the name of the php script as a command line argument, and not have the script generate any output that needs throwing away.
Advantage of the first method is that things like $_SERVER and server functions are available. The advantage of the second is that it's a lot simpler and requires neither a server nor a client.
Running PHP from the command line (a crontab is just a list of scheduled shell commands) is covered in the manual's discussion of PHP's [man]cli[/man] SAPI.
Of course, this isn't an answer to the question that was asked, because that has already been answered.