--passphrase.
To use the fpm image, you need an additional web server, such as nginx, that can proxy http-request to the fpm-port of the container. For fpm connection this container exposes port 9000. In most cases, you might want use another container or your host as proxy. If you use your host you can address your Nextcloud container directly on port 9000. If you use another container, make sure that you add them to the same docker network (via docker run --network ... or a docker-compose file). In both cases you don't want to map the fpm port to your host.