I saw a post on Facebook recently. A good friend complained that she was the only person who could see any of her posts when she posted from her iPhone.
I hope this will help her out. Here I am creating a new post on my iPhone:
If you look just above the keyboard, you will see icons that allow you to add people you are with, a location, or a picture. There is another icon all the way on the right.
If you touch this icon, you can set the audience for this post.
I generally set my posts to be seen by Friends of Friends.
After this is set, all new posts will be for the same audience.