Be aware that this can be security problem if you increase the session lifetime on a productive machine. Just do it on your local development machine where the database does not handle any sensitive data or informations. So far for the service announcements .
Are you tired of logging in every 30 minutes to the phpmyadmin (currently it is unimportant that there is a mysql cli and tools like tora outside)?
Just edit your configuration file. This file should be in the path "/etc/phpmyadmin" (on debian) and is called "config.inc.php". In this file, you just have to add the following line to increase the session time to four hours.
$cfg['LoginCookieValidity'] = 14400;
You want to know more? Take a look at the phpmyadmin wiki