There are practical differences - phones store a lot more information that you will keep in your mind at once.

You can actually eliminate phones entirely from your second example.

If you had incriminating info on paper at one point, and memorized it and deleted it, it would now be legally protected from being accessed.

One reason society is okay with this is because most people can't memorize vast troves of information.

Otherwise, the view here would probably change.

These rules exist to serve various goals as best they can. If they no longer serve those goals well, because of technology or whatever else, the rules will change. Being completely logical and self-consistent is not one of these goals, nor would it make sense as a primary goal for rules meant to try to balance societal vs personal rights.

This is, for various reasons, often frustrating to the average HN'er :)