Accused of cheating, without anyone witnessing it?
You admit that you knew that phones were not allowed in the testing room (being realistic, that they were not allowed on your person/in-plain-sight) during the exam. Yet the fact of the matter is that you had your phone out in-plain-sight, in the testing room, during the exam. 

The short answer here is that there's isn't much you can do -- it's your word against the TA's, and unfortunately the evidence is not in your favor. I believe that you're being honest -- but I'm a random individual on the internet. And even if your professor/instructor/department believes that you're being honest, they can still fault you for having your phone out, period.

So the only advice I have: be honest, acknowledge that you made a poor decision but deny that you were actively cheating, buy a cheap $10 watch, and accept that there isn't much you can do here. Best-case scenario is that you get a stern warning; I can't tell you if that's likely or not. There's a variety of worst-case scenarios -- I'm sure you know that though.

As for the individual questions at the end of your post:


What are my options here? Be honest with your department. Study up on your school's honor code violation policy and be aware of the possible proceedings, as well as your rights as a student.
How are they possibly going to accuse me of cheating when it never happened? You had your phone out during an exam when you knew you shouldn't. That alone might be their motivation. As to "how" -- again, read the honor code violation policy to see what official actions they would have to take.
I've been thinking of witnesses... This may be helpful in an official proceeding, but only if these women can explicitly testify that you weren't cheating. Which, unfortunately, is unlikely if they were focused on their exams. In any event, I wouldn't bring this up in the meeting with your department.
The other thing that worries me is that I usually answer questions very nicely and sometimes word for word. Could go either way. You're not that different from a lot of students most likely -- but they could also cite this as evidence that you were reading the slides on your phone. Unfortunately, not much you can do about that now.


Mistakes happen. If this is your first run-in with the school's honor code, odds of it destroying your future are slim -- I'm not sure I've heard of someone being suspended or worse on a first offense. But make sure you learn from this experience -- that's about all you can do now.