In a previous post, I detailed how to Use NGinx to serve static files and Apache for dynamic as well as the minor tweaks you need to make to have it work nicely with Joomla.
One thing I didn't cover, though, is setting up PHPMyAdmin. This documentation isn't going to go into the detail of installing and configuring PHPMyAdmin as there's plenty of that available elsewhere on the web. What we will discuss, though, is the NGinx configuration changes you need to make to have the connection reverse proxied to Apache.
These steps only really apply if you've gone for a system-wide installation of PMA. If you've unpacked into a web-accessible directory then you probably don't need to make any changes!