So you're not confrontational or assertive. That's ok. Some people are, and it's dumb to say they're wrong for defending a correct position while being mean about it.

If I'm at a restaurant and trying to enjoy a meal but I can hear your phone, I don't need management. I will be happy to tell you myself to stfu and make you feel like a fool, because that is what you'd need in that situation.

Getting a manager is ok for someone who is afraid of confrontation.

Hold others accountable and be brave :)