Blank php pages are usually due to fatal php parse or run-time errors. They could also be due to code that doesn’t output anything or the page got requested without invoking the php language (in which case the raw php code was output to the browser.)
What does the ‘view source’ of the page in your bowser show?
To get php to report and display ALL the errors it detects, set php’s error_reporting to E_ALL and set display_errors to ON, preferably in the php.ini on your development system. Stop and start the web server to get any changes made to the php.ini to take effect and check using a phpinfo() statement in a .php script that the settings actually got changed to those values.