How can I create a phpinfo.php page?

To create the file simply add the following lines of code to a blank document and name the file phpinfo.php

Save the file as phpinfo.php and place it in the desired directory. Lastly, call the script from a browser.
Example: http://www.example.com/folder/phpinfo.php 

The phpinfo file outputs a large amount of information about the current state of PHP. This includes information about PHP compilation options and extensions, the PHP version, server information and environment (if compiled as a module), the PHP environment, OS version information, paths, master and local values of configuration options and HTTP headers.