Is there a reason we can't add new tags when using the mobile site? Is this a bug or a feature that is yet to be implemented?
Is it possible to get it added?
The answer can be found on meta.stackoverflow.com
It appears that this is a deliberate design decision, and has been since the mobile site was launched (or at least October 2011 when the question was answered).
Its unlikely they will add this feature, as StackExchange are investing in developing iOS and Android applications, and are likely to want to concentrate on those rather than enhancing the mobile site. The iOS application is in private beta as we speak.