I start sketching with a blue pencil, and clean up the lines with a black pencil. I then scan the drawing at high resolution (300~1200dpi) with my Canon flatbed scanner (Irfanview and VueScan scanner driver). VueScan, while not free, allows me to use my Canon flatbed scanner with Windows 10, and the scan quality is excellent (way better than the original Canon drivers ever were).
Next, I open the result in either Krita or PhotoLine for cleanup. Then I start inking and/or colouring/painting in Krita and/or ClipStudio.
Check out David Revoy's step-by-step explanation for more info:
http://www.davidrevoy.com/article239/cl ... h-in-krita
He has the scanned artwork available for download, so you can test it for yourself.
Taking photos with your phone is not suitable with this approach. The lighting and camera quality/sharpness is too limited - even a high-end DSLR requires a stable setup with good even lighting to work. I suppose tracing might work to just get your basic sketch as a guideline, but if you are serious about converting your paper artwork you MUST get a flatbed scanner.