...
ffmpeg -i "[your rtsp link]" -f flv -r -s -an "[Your rtmp link]"
If the IP camera has the ability to push RTSP, point it at the container at https://hub.docker.com/r/aler9/rtsp-simple-server. Phenix can then pull the content from that container.
Alternatively, if the camera is a private IP camera with RTSP, set up a process to pull the RTSP from the private network and publish it to the https://hub.docker.com/r/aler9/rtsp-simple-server docker container on a public network (like a DMZ) where Phenix can access it using a command such as:
ffmpeg -re -i "[the input rtsp link]" -c copy -f rtsp rtsp://host:8554/mystream