i have setup an mariadb server, and now i want to install/use phpmyadmin with the internal webserver of the pi-hole.
i want just call phpmyadmin via http://ip-of-pi/phpmyadmin (there is no need of an dns-entry), and i need an "whitelist-entry" for it.
the files are saved under /var/www/html/phpmyadmin
the user+group are set to www-data:www-data
permissions are set to readable
my /etc/lighttpd/conf-available/99-external.conf is in the moment (yes, it's enabled via lighty-enable-mod external):
I didn't test anything, but I think your configuration is not executing PHP files in /phpmyadmin path.
Pi-hole default config only configures PHP for the /admin path.
You need to add PHP (fastcgi.server block) configuration for the /phpmyadmin path.
Something similar to this block, but using a different socket file and probably passing different environment variables: