This has been an ongoing teeth-gritting, temperature-raising situation for me.
Every time BIL's family comes over for, granted, a very informal meal, she just seems to be constantly on her iPhone, whether it is sending texts or using the apps.
I would mention it very pleasantly, and in a joking fashion, but I am just concerned that as her mom doesn't tell her not to, it's not really my position to override her mom's parenting skills.
So, AIBU to gently and teasingly ask her to put it down while we are sitting eating?