If you've installed my e-smith-php4 package, Apache should already accept index.php as a Document Index. Otherwise, if you're doing it manually, you can either
1. Change /etc/e-smith/templates/etc/httpd/conf/httpd.conf/50DirectoryIndex00 to add index.php as a valid index file, or
2. Add /etc/e-smith/templates/etc/httpd/conf/httpd.conf/50DirectoryIndex01-php with a second DirectoryIndex statement to add index.php.
The second is probably the better solution.
Having done either of those, you'll then recreate httpd.conf with
# /sbin/e-smith/expand-template /etc/httpd/conf/httpd.conf
and restart apache with
# /etc/rc.d/init.d/httpd restart