I added AddType application/x-httpd-php .phtml into httpd.conf but still have a problem
Did you restart Apache after doing that? Also, is the behavior your seeing the same as before?
What happens if your try to access http://localhost/joomla/index.php?
Finally, have you added any modules to Joomla? If you have, it might be a good idea to remove them and make sure that the base Joomla is working properly.