Hi Viv,
I agree that this website is an attrocious design, and have posted to that effect a few times in the community, and thare are many others making smilar comments. BUT, it does work, and if you take a little time you can work most things out even if it is obscure and not very intuitive. Regarding seeing availability, there are a lot of "part-time" hosts on Airbnb who only let a room or whole house/flat out at certain times, say when they are at home, or when they are away. I think you might be misreading the information on the calendar, or the host you are looking at has blocked out the dates because they are not making it available, rather than that is booked out till 2022, for example.
As far as a contact phone number, I am not going to give you one, but it is not difficult to find the Australin number via Google. I have had to ring them to find out something, & found the phone staff quite helpful.
Regarding the process to list on the site, how would you like it if someone else (anyone) could easily impersonate you and/or the ownership of your property and list your house or room as available for rent on Airbnb and even collect a bookings fee even if fraudulently. The first you would know is when someone turned up demanding the bed or whatever that they believe they paid for. AND, Centrelink & ATO (all linked) holds far more personal information on you than Airbnb, believe me, and anyone else you care to ask !!!!! If you are only using the site as a guset, then the same principles apply. Would you like someine to turn up to stay in your property who you have never met or had anything to do with before without having their identity checked out as thoroughly as reasonably possible? I think not. In most if not all Australian states, by law, a commercial rooming establishment (hotel/motel etc) is required by law to verify the identity and record it of anyone staying before they let you in, and they can refuse you entry if they have any doubts. While no doubt there are people who will try & beat the system, I for one as a host am all in favour of having the best sytems possible, and I think Airbnb does this as well as any other site if not better than most..... even if it is convoluted.