I can go to the Multiplayer Menu and then Go-Online. I answer to some questions regarding User Name, Password etc.

Some times it gives me an error (related to my ROUTER) which -to be honest- I can not understand.

I posed the question also to PHOENIX TECHNICAL SUPPORT and the answer is really very interesting:

Hi George
This competition mode (mean Streamer Cutting) is currently only available if you are in a multiplayer session, or have another pilot with another Phoenix USB interface connected to your computer (split-screen).
However, we are very close to releasing the BETA of the next version of Phoenix, and this update does allow you to use this mode against an AI-controlled opponent.

Best Regards
Phoenix Support

So, we will wait for this Version. I believe that this option will give us enormous abilities to exercise a Combat without going to the field (and without loosing planes of course!)

Regards

George