Try looking at https://www.openstreetmap.org/way/863780195 on a cellphone.

As you observe the map is never going to get bigger than half the screen.
But wait, there is a very very light colored gray X that we can press that will perhaps get rid of that big white panel.
Alas, when we press it it also gets rid of our way!
The problem is that you have the accessibility scaling settings turned up to the max, which is fine and dandy, but once you've run out of screen real estate, as in this example, things will break. Larger elements are actually larger.
Some of the breakage could probably be fixed (the layer selector doesn't scroll over its full height for example), but essentially you would need to completely redesign the whole layout to get anything close to workable. For example the buttons on the map display would have to be handled very different so that they remain accessible and so on.
Maybe for now there could be a way, when viewing individual nodes, way, relations, to get the whole left panel moved off the screen if somebody wants to. Just like one can do with the left panel in the iD editor. Not only would this help out when viewing something on a cellphone, it would also help out on desktop too. Sure usually we want that left panel but sometimes we want a bigger view.
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The problem is that you have the accessibility scaling settings turned up to the max, which is fine and dandy, but once you've run out of screen real estate, as in this example, things will break. Larger elements are actually larger.
Some of the breakage could probably be fixed (the layer selector doesn't scroll over its full height for example), but essentially you would need to completely redesign the whole layout to get anything close to workable. For example the buttons on the map display would have to be handled very different so that they remain accessible and so on.