Is the phpMyAdmin page actually blank (as in a completely white page, no text, no images), or does it have a username and password box and some other output, but no listing of the account's databases? The reason that I ask, is in the instances I am familiar with, the phpMyAdmin page is not "blank" per se, but has fields for a username and password and does not list the account's databases, and at the same time the error in the first post in the ticket is logged to /usr/local/cpanel/logs/error_log. I just wanted to make clear to everyone that the problem we are discussing is not usually a blank page, but a page that does not contain the usual phpMyAdmin output we expect.
I have attached a screenshot that shows what is often described to us in tickets as a "blank" page. If you see this page, before you start a forced update of cPanel (upcp --force), reset the cPanel account's password. That may be all you need to do.
In most of those instances of this problem that we have seen, the MySQL database user's password was not in sync with the cPanel system user's password, and resetting the password was all that was required. After you reset the cPanel user's password in the WebHost Manager, log out of cPanel and log back in, and then click the phpMyAdmin icon again.
If resetting the cPanel account's password does not correct the problem, submit a ticket, as Michael suggested, so that we can look at the specific problem on your server directly.