You could change the listening port of the Apcache in /etc/apache2/ports.conf (depending on OS). BUT this Apache instance would just run inside the docker container and will not automatically be reachable on this port from the outside (host). You can set the listening port to whatever you like, but it’s the “port-mapping” between the host and the container that is crucial.
So leave the apache running on port 80 and change the port-mapping when launching the container:
docker run --name myApache1 -p 9090:80 -d < ID of Apache Image>
This docker run will start an Apache Image and map the port 9090 on the host to port 80 inside the container.