I don't know cell phone view, but one issues some people have had is attempting to post to a category and not a forum.
So for example, maybe they want to write about planting barley. That's about growing things so they go to the growies category. Only they don't see that there are several different forums in that category. If they go one level further and click on grains then they can start a new thread.
Or it could be something else.
You were able to start this thread okay. Were you writing it on your phone? What forum are you wanting to start your thread in?