I made this design to use in a school project, and it worked good enough for me to consider sharing it with other people as well.

The file consists of several, separate parts, which can then be put together to make the phone stand. There is a knob on the side which you can turn to rotate the gears, which in turn rotate the phone holder.

If you would leave it there, there would be no resistance to keep the phone from falling either forward or backwards, as the gears can still rotate freely. To keep your phone in the right position, you can slide the last part over the ridge on top of the part in which the knob is situated, which will lock the gears in place.

When putting together the phone stand, some parts have to be pressed together, and are designed to be friction fit. If some parts are hard to connect, you can try to sand them to where they do fit together. If some parts are loose, you can apply a little bit of glue to secure them.