The problem is that the required line in the Apache configuration file that can serve webpages for phpmyadmin is not included. Here are some commands you should type in terminal to fix this:
sudo dpkg-reconfigure -plow phpmyadmin
This command configures the installation of phpmyadmin and copy the file for phpmyadmin to the correct path.
Then check again the configuration.
grep phpmyadmin /etc/apache2/apache2.conf
And reload apache again
sudo /etc/init.d/apache2 reload
If the all commands above is unsuccessful, type the following commands:
sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf.d/phpmyadmin.conf
sudo /etc/init.d/apache2 reload
And check your browser one more time: localhost/phpmyadmin
It should work....
