Seriously, is it justifiable to ignore a patron clearly waiting at the counter to pay for her chocolate milk while she's talking on her phone to a colleague, friend or family member while she waits? Does she really have to wait over 5 minutes while three people behind the counter look past her and then get a lecture when she says loudly that she "just wants to pay for this milk"? She just wanted the damn milk! Don't tell her it's rude to be on the phone when you don't even know why she's calling/being called for. It could have been an emergency and she needed that milk for someone. Who even cares why the hell she was on her phone, she just wanted service and to get out, and you idiots ignoring her wasn't helping her, her situation or her mood and she walked out looking very pissed off. I serve people on their mobiles whenever I get them, they're either relaying an order or taking an important call and she may have been doing the same. Maybe she NEEDED to get out and you made her late for something.
It is NOT good service, nor worth the loss of business when you get snarky at her and bitch at her for being rude while she's on the phone. She can blame you if she was late for work or another event she was needed for or if something happened while she was in there waiting to be served that could have been prevented if you'd served her as soon as you saw her. Phone to her ear or not. Ignoring her for being on her mobile and lecturing her about it was much ruder and out of line than her being on her mobile and a huge inconvenience. It was very rude to ignore her while she was taking a call.