On an iPhone or iPad, open the Files or Notes app and use “Scan a Document” to scan a document with your device’s camera. On Android, use the Google Drive app to scan a document to your phone or tablet. (The Google Drive app works on iPhone and iPad, too.)
These existing apps actually do a very good job of scanning multiple pages, straightening pages, recognising the text, using existing storage, etc. There is no reason really today to go buy scanners or even 3rd party apps.
See https://www.howtogeek.com/209951/the-best-ways-to-scan-a-document-using-your-phone-or-tablet/