There is another similar question for an older version of Android and instructions here for Android 6.0 but neither work, plus I would like to have the entire phone connected, not just the MicroSDHC card.
How can Android 7.0 be force to automatically connect as USB Mass Storage Device?
It would be nice to have solutions for both standard and rooted phone but mine is currently rooted.
Right now, it is a pain since it automatically connects for charging and one must unlock the phone to get to the notification to open the list of options to select Use USB to Transfer Files. This is too much work as the only reason I am connecting the phone to a computer and not a charger is to get files.