First of all, there is no one universal PHP.INI file. This is the whole point: to configure PHP according to the requirements of particular hosting or each individual site. If such universal PHP.INI existed, it would not be even exposed to the user, as all the data would be internal to the product and configured by the installer.
So, you need to 1) get relevant information from hosting provider, 2) learn how to configure PHP via PHP.INI; this you can do by installing PHP locally for learning purposes and reading: 2a) PHP.INI comments in this file, 2b) PHP documentation; please see:
http://php.net/manual/en/configuration.php[
^],
http://php.net/manual/en/configuration.file.php[
^],
http://php.net/manual/en/ini.core.php[
^].
—SA