The (fairly) new mobile layout is great and very functional. However, it seems there's no "close" link next to "edit" and "flag" when viewing a question. The flagging interface works just fine in the mobile site, so I would think the vote-to-close interface could be easily done as well. However it's simply not there. Is this by design or just in the works?
While it was possible to vote to close before, via the flag link, we've recently deployed an actual "close" link on the mobile theme.
We may have to go back on this in the future. We're absurdly cramped for space already, and if we absolutely need it in that menu, "close" will be first on the chopping block.
For now though, it's available.
I could have sworn that this came up recently, but I'm unable to find the post. Assuming my memory isn't playing tricks on me, I seem to recall a developer mentioning that the mobile interface was optimized for the most common use cases, which may or may not include voting to close questions.
In either case, the "it does not belong here" flag option will load the exact same dialog as you'd get from the normal close link, so if you're intent on voting to close from the mobile theme you can still currently do so: