you can use the backtick notation:
`php file.php`;
You can also put this at the top of the php file to indicate the interpreter:
#!/usr/bin/php
Change it to where you put php. Then give execute permission on the file and you can call the file without specifying php:
`./file.php`
If you want to capture the output of the script:
$output = `./file.php`;
echo $output;