The "Connection for controluser as defined in your configuration failed" problem can be eliminated by refreshing the configuration of the the phpmyadmin package.
Open a terminal window by clicking the terminal icon to the right of the colorful Chrome icon near the lower left corner of the appliance screen. In that terminal, run
sudo dpkg-reconfigure phpmyadmin
In the resulting configuration dialog, you move among the field on each screen by pressing Tab or Shift+Tab. On some screens, you can just Tab to highlight your answer (such as Yes, or Ok) and then press Enter/return to move to the next screen. On other screens, you will need to select and option or type in text before tabbing to the Ok "button" and pressing Enter/return.
Here are suggested answers:
- Reinstall database for phpmyadmin? Yes
- Connection method for MySQL database of phpmyadmin: Leave "unix socket" selected, then Ok
- Name of the database's administrative user: Leave "root", then Ok
- Password of the database's adminstrative user: Type crimson, then Ok
- MySQL username for phpmyadmin: Substitute pma for phpmyadmin, then Ok
- MySQL database name for phpmyadmin: Leave "phpmyadmin", then Ok
- Web server to reconfigure automatically: Leave "apache2" checked, then Ok
The dialog will close and the web server will be restarted so that the changes take effect.