The point is that it's as convenient as a phone. A sleeve would nullify this. Might as well get a tablet.

My pocket is already a sleeve, because I don't carry anything else in the pocket where I carry my phone. But the problem is that I drop the phone occasionally (for me, it happens maybe once in a half a year, but it would be cumbersome to replace the screen every half a year, so I use a protective case).

You could use a sleeve, I guess, but I’ve never seen anyone carry their phone in a sleeve.

You can not use a folio case because the screen is on the outside. You have to remove the phone entirely from the case to unfold it.