I empathize with you. As students, it is hard to know what to expect going into a clinical situation. Every preceptor is different, and we have to figure out their personality, learn their communication style, and learn what they expect from us. We have to do this quickly, right at the beginning of our clinical, and sometimes (like your situation) we only have one day, so there is no room for error. The preceptors then evaluate us based on the temporary relationship they had with us. And our instructors rely on the preceptor's point of view, because they are not there to see what actually happened. It's a horrible feeling to think the day went well and then be blindsided by a complaint.
It's true that some preceptors are unfair in their evaluations, and some are not good mentors to start with. (Just like there are bad students out there.) Maybe this nurse could've handled the situation better. Maybe she was stressed and distracted herself because of having to take her daughter to the doctor. But I would NOT address it with the clinic nurse. You'll make the problem worse. Don't do that. Unless you will have a long-lasting relationship with this nurse, in which case I would approach it as apology/explanation/won't happen again/thanks for your time.
That being said, cell phones are almost always a no. My school has given us strict warnings about it. The only time I would pull out my cellphone is if I had double-checked with my instructor/preceptor to explain that it was a good reason and make sure that they were ok with it. (And I know you were studying for a test, and I definitely understand the downtime problem. But you know what I mean?)
Don't let it worry you too much.