Please be aware that normally one does not have issues like this when setting up phpmyadmin from synaptic. I have setup many system over the past years with PCLOS and myphpadmin and have not yet once encountered the issue you are having! This is not the norm.
By any chance did you use either a "@" or a "!" in your password when setting it up? myPHPAdmin don't like them in a password.
You might try the following
in a console (terminal) window type in the following, where NEWPASSWORD is the password of your choosing.
$ mysqladmin -u root password NEWPASSWORD
and than login to phpmyadmin using 'root' and your newpassword.
If that doesn't work then you could change the config.inc.php file. In a console window, as the root user, use the command
locate config.inc.php
you should see something such as
[root@pclosusers youcantoo]# locate config.inc.php
/home/members/linuxguy/phpmyadmin/config.inc.php
/home/members/scripts/php/myadmin/config.inc.php3
[root@pclosusers youcantoo]#
then open your favorite editor in superuser mode and edit the following line
$cfg['Servers'][$i]['password'] = ''; // MySQL password (only needed
// with 'config' auth_type)
you will need to add your password like this
$cfg['Servers'][$i]['password'] = 'MYNEWPASSWORD'; // MySQL password (only needed
// with 'config' auth_type)
Make sure there is a single quote mark on both sides of your new password.
Save the file and try logging into myPHPAdmin and see if that works for you