I followed the ISPConfig 3.1 manual to install a multiserver setting (on Debian 8) but I can't access to phpMyAdmin from the link in the database section in the ISP console (actually can't access directly either). The link from the console points to https: // server.tld:8080/phpmyadmin. I tried with http: // server.tld:80/phpmyadmin but the URL is rewritten to https: // server.tld:80/phpmyadmin and the browser gives an ERR_CONNECTION_CLOSED message.
The link in the ISPConfig interface is configurable, so you need to find what url works and put it in there (as an example, on a multi-server install I have phpmyadmin installed on each webserver and use https://[SERVERNAME]/phpmyadmin so each client hits the server hosting their site - and the webserver is also the database server). You can't https to port 80, try just https://server.tld/phpmyadmin and see if that works.
