Hello, I have a bit of a complex question.

I do almost all of my maps in mixed media, starting with traditional drawing on A4 paper, inking and then continue to PS to polish it and colour it. I've had some issues with my scanner so currently I am mostly taking photos of my maps with my phone and using that as a reference point while working in ps. I've noticed that the quality drops significantly when I do that, so I was wondering if anyone had any suggestions how I could increase the resolution and quality of the final map?
And what are your usual go to sizes and resolutions when mapping?

Thank you in advance.