But really your looking for a way for the central phpmyadmin server to securely access the mysql instances on the various VPS. Sorry about that.

Merging MySQL Tables With phpMyAdmin. PhpMyAdmin is used as the backend database interface for a number of leading content management systems deployed by businesses, including WordPress, Joomla ...

Jack Wallen walks you through the process of enabling configuration storage for phpMyAdmin to gain added security features for the web-based MySQL tool.