How do I open a TCP port on a Ubuntu physical machine (host) for a Win virtual machine (guest)?

To figure out what's going on, you can check the iptables for any firewalling with the command iptables -L -v

And ports that are listening for incoming connections with netstat -ltp

For example, it might be that you're listening for connections on a different interface (ip address) than the virtualised machine is connecting to.