since administration of the web server is not my major goal I wanted to quickly solve the problem with getting the phpmyadmin from other IP addresses than localhost.
So here it is:
Step1: Copy the entire phpmyadmin directory to the htdocs (=root)
Step2: Rename this newly transferred directory to something else.
This is the way how to get arround the security block when accessing the mysql.
PS: No changes are necessary in httpd-xampp.conf at all, no restarts.