1. Create a file where webserver can write

#touch /home/path/public_html/php_errors.log && chown -R 777 /home/path/public_html/php_errors.log

2. Create or add the following lines on .htaccess file

php_flag log_errors on php_value error_log /home/path/public_html/php_errors.log

It also possible with enable the same values on php.ini file.

A sample .htaccess file will look like this

php_flag log_errors on php_value […]