Resolution
POA allows Provider to configure php.ini settings using Control Panel providing the easy way to manage setting per specific hosts or for the whole installation.Log in under admin account to POA Control Panel, go to Top > Deployment Director > Application Manager > Services > apache > Configuration tab
Here you can choose the existing or create new Apache service configuration per your needs and by host attributes.
Click on "Apache service default configuration" > then switch to the tab "PHP Configuration" > finally press the "Edit" button on the necessary subtab to configure required settings.
Once you have finished configuration go the "General" tab and press on "Apply Changes" button.
Note: in case you need to disable specific PHP function, e.g. due to some security reason, you have to set "safe_mode" to "On", else the screen with disable_functions field is not displayed.