From the documentation:
$cfg['Servers'] array
Since version 1.4.2, phpMyAdmin supports the administration of multiple MySQL servers. Therefore, a $cfg['Servers']-array has been added which contains the login information for the different servers. The first $cfg['Servers'][$i]['host'] contains the hostname of the first server, the second $cfg['Servers'][$i]['host'] the hostname of the second server, etc. In ./libraries/config.default.php, there is only one section for server definition, however you can put as many as you need in ./config.inc.php, copy that block or needed parts (you don't have to define all settings, just those you need to change).