Can't connect to a remote server using phpMyAdmin
Check your PHP version (and in particular, your PHP MySQL connector version), it may not have support of the newer authentication plugin. If for some reason you cannot upgrade you client PHP installation, you can change the user you are using to connect on the server to revert back to the more insecure native authentication so it works with older connectors, but try to upgrade the client first.

More info:


http://blog.ulf-wendel.de/2012/mysql-5-6-sha256-secure-password-support-for-php-mysqlnd/
https://dev.mysql.com/doc/refman/5.6/en/sha256-pluggable-authentication.html
https://stackoverflow.com/questions/30710146/php-mysqlnd-sha256-password-plugin-access-denied-user-works-from-cli-mysql