On the iPhone app in portrait (at least on an iPhone 6 or smaller, it's probably not an issue plus size models) the "close" link is hidden behind the "more" button:
On the site however the "close" link comes before "flag":
Changing the order for consistency with the site would have the added benefit of a smoother user experience when close voting from the app. Not only would this save on an extra tap and UI to get to the close screen but would show you the number of existing close votes without having to actively go looking for it (as the site does).
It is possible to close by using the flagging dialog, which gets around the issue of extra taps, but that still hides the current vote count and probably isn't known by a lot of users. Flagging should be used as a last-resort option so using the flag dialog as a vote-by-proxy is encouraging the wrong behaviour and confusing.