Can you go to the lobby to use your cell phone during the concert?

Yes

Yes. You are given a bracelet for the concert and one for booze, and as long as you don't exit the facilities, you're free to free to move about as you please.

Yes. If its still too loud, staff informed us that you may exit and re-enter once the main artist / headliner has started as well, but not before.

Not sure, but the area near the bar and bathroom are usually quiet enough for you to talk on your phone/others!