If you are working on your local box, phpmyadmin will expire the session every 1800 seconds which is 30 minutes. sometimes that just too soon, so you can hack it by change the value of $cfg['LoginCookieValidity'] in /usr/share/phpmyadmin/libraries/config.default.php

i usually set it to 18000…

$cfg['LoginCookieValidity'] = 18000; // validity of cookie login
// (in seconds)

I usually set this and forget it but it always takes me like 4-5 minutes to FTFSC and find where to set it again..