There's a report[1] from a user who recently upgraded to PHP7 and is getting the Cannot log in to the MySQL server error message with phpMyAdmin. He's done quite a bit of troubleshooting and I don't see anything obviously wrong with his setup. I'd be delighted if some other developers could look over the question and see if they can find some hint here.

Thanks

1 - http://stackoverflow.com/questions/33897389/phpmyadmin-cannot-log-in-to-the-...