This theme is called pmamhomme because the theme designer is Mike Homme.
First, grab the pmamhomme theme (.zip) from phpmyadmin.net’s theme page.
Next, unzip this in phpMyAdmin’s theme directory. In Ubuntu or Debian, this directory is located at:
And finally, once the theme is unzipped in the theme directory, simply choose pmamhomme inside the phpmyadmin app.
Here is how it looks!