Adobe scan is a free smart phone app [download here] that creates perfect scans of 8.5x11 rectangular paper sheets photographed on a dark background so the app can automatically find the sharp rectangular edges of the sheet and then correct for its quadralateral shape from the camera angle, while ignoring light shadows from bad lighting. Of course it works on any rectangular shape as well.
When you center your scan sheet in your camera window and press the camera icon in the app, a blue outline appears with bullet circles at each corner which guesses at the rectangular region you want to scan and usually does an excellent job, but once it takes the scan, you can adjust the corners to correct for a poor border. Then save the scan to PDF, also to JPG if you wish next. Then Share it via email with yourself so you can download on your computer, or share directly via your phone options for sharing.
It takes only a few minutes to download and install and set up this free app. You can uncheck OCR character recognition to avoid having to skip this with your completed scan (it makes an editable file if you can something printed). It produces a single PDF of the pages you scan together, then you share it with yourself via email to transfer to your computer where you can rename it and use.
I never use a flatbed scanner anymore for all my academic scans. For photos at home, yes, I use my flatbed scanner.