You either need to compile PHP as an executable so you can run scripts from the command line, or you can use a command line browser such as "lynx", "links" or "wget".
In the first case, PHP, normally compiled as an Apache module, will only run PHP scripts when directed to by Apache. You have the option of compiling PHP instead as a stand-alone executable that can run PHP scripts outside of Apache. If you did this, you would change the crontab command to:
/path/to/php phpfile.php3
The second option is a little easier, it is basically automating someone hitting the web page. You probably have some kind of command-line web browser on your system, like "lynx" or "links", or something that can fetch web pages from the command line, like "wget". You'd change the crontab command to:
/path/to/program http://localhost/x.php3
or something like that, whatever URL you would use to access the script through a web browser. You'd probably need to mess with the command-line options of "links" or "lynx" to only fetch the page and then exit, and not enter some kind of interactive mode.
