By default ispCP uses FastCGI and because of that every domain has it´s own php.ini.
You can find the php.ini for the user-domain example.org here: /var/www/fcgi/example.org/php5/php.ini
You can find the php.ini for the ispCP virtual host here: /var/www/fcgi/master/php5/php.ini
If you use PHP4 instead of PHP5 look into the php4 directory.