How to Enable PHP Error Logging
sudo vi /etc/php5/apache2/php.ini
error_reporting = E_ALL | E_STRICT
error_log = /var/log/php_errors.log
You must create the (log) file manually
touch /var/log/php_errors.log
chown www-data: /var/log/php_errors.log
chmod +rw /var/log/php_errors.log