Authentication and Security - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 29

With no default server defined, phpMyAdmin will present a server choice:
Arbitrary server
Another mechanism can be used if we want to be able to connect to an undefined
MySQL server. First, we have to set the following parameter:
$cfg['AllowArbitraryServer'] = TRUE;
We also have to put back the default value of 1 into $cfg['ServerDefault'] . Then,
we need to use the cookie authentication type. We will be able to choose the server
and enter a username and a password.
Allowing an arbitrary server means that any MySQL server accessible
from our web server could be connected to via phpMyAdmin. Therefore,
this feature should probably be used in conjunction with a reinforced
security mechanism (see the Security section).
As seen here, we still can choose one of the defined servers in Server Choice . In
addition, we can also enter an arbitrary server name, a username, and a password:
As the tooltip indicates, you can also enter a port number (of course separated
from hostname/IP address by space), if this MySQL server is listening on a
non-standard port.