I think a 'are you allowed on your phone while you are serving?' question would be good - she then says sorry and hangs up or explains it was an urgent call (yes I know it was about holidays but change of flight times or something)
If you got no response from that, then report to manager - I would do it in writing - either one of those feedback forms if they have them or a letter or email to the store - with details of time, which checkout etc and the persons name if they were wearing a name badge.
Keep it polite and to the point.
Did you think you were poor growing up?
Has anyone played That’s Not My Neighbor? Surprisingly tense little game




