[ I saw this question; but I think that is a different thing; or to be precise: that question says "fixed"; but not in the way that the question suggested ]
There are few things that also work nicely when browsing SE sites on a mobile device; for example: putting in close requests.
That is unless one decides to do a "close as duplicate". Because in that case, I first have to select the question to "dup" to ... and then click the "Vote to close" button ... which is below that question.
So what happens is: a potentially huge question is fully displayed; and I have to scroll down forever in order to get to that button. But most likely, I already know that this is the DUP question I want.
In other words: why not move that button above the section with the suggested DUP questions? That would make the whole process much more mobile-friendly (and I don't see that it would make the desktop experience any different - even to the contrary; as that button could simply stay in its place all the time): I turn to that page; I get a list of potential candiates; I select the one I want; I press the "Vote" button. No scrolling required (unless I really want to look into that DUP question)