Once installed, the dashboard page can be found at
dashboard/system/environment/phpinfo.
In the dashboard menu, select 'System and Settings' and then look for PHP Info under the Environment group.
The page gives options to show phpinfo() for the categories:
Use the 'Plain Text' button to toggle the output to plain text for copy/paste to emails, forums, bug reports and support requests.
On some web servers the page may show an error message "Unable to find body of phpinfo response. The addon code may need adjusting to work correctly on this server.". There are two main reasons why this error message could occur:
In either case, an essential diagnostic is to try and run phpinfo() directly as a self-contained script. Create a file called phpinfo.php and upload it by ftp to the root of your web server. The file should contain only:
<?php phpinfo(); ?>
When you have finished, always remove the above file from your server. Leaving direct access to phpinfo() can open a serious security breach.
I cannot do anything about (1), that is between you and your web host. I may be able to update this addon to handle (2). You will need to 'save' the web page output from directly running phpinfo() as a file (not as a screengrab - I will need to see the raw html from the page), zip the file up and attach it to a support request. If you are a developer, feel free to save me time by suggesting changes to the code.
See http://php.net/phpinfo for more details about the information provided.