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!