As usual, phpMyAdmin would be automatically logged in from within cPanel that you would only need to be logged in cPanel to access phpMyAdmin without providing any MySQL username and password. However, sometimes, this automatic login breaks and need to be fixed.

How?

The reason for this issue is that your account's MySQL password has gotten out of sync with your cPanel account password. I went ahead and synced those passwords for you. Please log out from cPanel, clear your browsers cache and try again. Most browsers well let you clear the cache by pressing ctl+shift+del or you could force your browser to reload the page without the cache by pressing ctl+f5 (these work on Firefox and chrome, I'm not sure about Internet Explorer). If you need to sync the cPanel and MySQL passwords for the other accounts please follow the following steps:

1. Login to WHM.
2. Navigate to Main >> Account Information >> List Accounts.
3. Next to the cPanel user you wish to sync the password for, click on the little box with the "+" sign located all the way to the left.
4. Ensure that the box next to "Sync MySQL password with account password" is checked.
5. Enter your new password and click "Change".
6. Don't forget to logout from cPanel and clear your browsers cache.

Now it should be fine.