This is quite easy, just add this to your PHP file:

error_reporting("E_ALL") ;

you can also achieve this via .htaccess if AllowOverride is set correctly:

php_flag display_errors off

 If you would like the errors to be logged to a file though, you can also do that:

php_flag log_errors On 
php_value error_log /var/log/apache2/site.errors.log