We will need:
Plywood
Three screws
Brackets (from my tablet case)
Fasteners for pipes (select according to the diameter of the steering wheel)
Bolt with nut.
Let's get started.
First you need to come up with a form for the holder. After that, draw a template on paper or immediately on plywood.
We cut out two blanks (one on the size of the phone, and the second a little narrower, so that the brackets are the width of the phone).
Now in a narrow blank (from the inner surface) below and on the sides we make slots for the brackets.
It will look like this.
In the second workpiece we make a hole for fixing the fasteners.
And with the help of a bolt and nut we fasten the fasteners to the workpiece.
Next, we collect both blanks and brackets using self-tapping screws.
It remains to cut a lining from foam rubber or other material so that the phone does not scratch, and it will protect it a bit from impacts.