How to assemble your smartphone?

Question

Batteries

I would really like to know how you can make your smartphone. Who to buy accessories from? Where to collect? The smartphone should be without a camera, with a slot for flash drives, with one or two SIM cards, 256-515 RAM, a speaker only for talking, a microphone, a battery, where you can order a case, for mass production, the price is $ 130-150. I am not a techie (almost a humanist), and in these matters a layman (~ 0).
You can also buy a smartphone from the Chinese, but I think it would be better to collect it from the Chinese themselves.
If you propose an idea to companies (for example, yota devices)?

Answer 1

A smartphone can be assembled on the basis of raspberry pi, such a project is called PiPhone.
All components can be bought in stores selling electronic components, or from the Chinese.

Answer 2

Why reinvent the wheel?