The two tags most commonly used with phone are windows (× 668) and android (× 465).
The 668 questions tagged windows+phone appear to be mainly misspellings of windows-phone, and should presumably be retagged accordingly.
There's currently no android-phone tag, but one could argue that something like that tag should exist, for the same reasons as why iphone is not a synonym of ios. That said, looking at the actual questions tagged with android+phone, they're kind of a mess — while a few of them might actually be about issues specific to Android phones (as opposed to e.g. Android tablets), most of them just seem to have the usual random assortment of poorly chosen tags.
The remaining 596 questions are a mixed lot. (When two out of the top three highest-voted questions are closed, that's pretty telling.) Many of these seem to be about phone number storage and validation; I'm not sure if these really form a useful topic for a tag, but we do have an existing phone-number tag they could be moved under. A few seem to be about programmatically making phone calls, for which we have the (pretty poorly named, IMO) phonecalls tag, and yet a few more seem to be about things like detecting whether a mobile device is a phone or a tablet and other odds and ends.
In any case, I do agree that this tag needs a thorough cleaning and blacklisting. I just wish there was some way to do the first step that didn't involve manually editing (and bumping) just shy of two thousand questions. We do have a write API now, so maybe someone will write (or has already written) a good tag-editing bot that could at least take care of the easy cases.
In the mean time, I believe it's technically possible to blacklist the tag now, to stop it from being added to new questions, and then let the cleanup proceed at whatever pace we can muster. Accordingly, that's the course that I'd vote for.
Ps. I noticed that there's also the essentially synonymous telephone tag with 77 questions. And the cellphone and mobile-phones tags aren't really in very good shape either, although they're at least slightly more specific.