When I use my phone camera to copy documents or especially photographs (i.e. old school printed-on-paper paper photos), I've found the most useful thing is to light it with the sun. You can do it next to a window if the sun is shining in (best the window is clean), or I just do it on my porch if it isn't windy. They come out with excellent quality...I have found it does better than even scanning them (which takes much longer)
Obviously, the sun should be at enough of an angle so it won't cause glare. You can try to position it so the sky isn't reflecting in the photo, but honestly the effect of that is going to be miniscule because the sun is so much brighter.
And of course, if you have to do it when the sun isn't out, you can make do with whatever lighting you have, but the quality won't be as good from my experience. I've done this for family photos from ages ago, and it wasn't a problem to wait for some sunshine.