I think you've actually missed an underlying point of the thread. I know you started it, so you feel like you know what you wanted it to be about. I agree with you, society has not adapted to people checking their watches when they should be doing something else. Thankfully, and hopefully it never will.
What you illustrated clearly in your OP is that there are members of society who think it's acceptable to use their phones whenever they feel like it. I'd like to point out to you that while you might feel this way, there are still people who don't. They think it's rude and impolite, and in the case of a store clerk using one on the job when helping a customer, completely inappropriate.
Just because your customer was in the store for 15 minutes and kept coming back and asking questions does't mean she would have been okay with you checking your phone or that she wasn't in a hurry. It likely just meant she wanted to make sure she got everything she needed while she was there. Even if she wasn't in a hurry, you are not being paid (if your father was paying you, but play along here) to use your phone, you're being paid to help customers.