Phone a Friend

You can set up the general context of the call ("I'm in a Magic game and I need someone outside the game to make a choice"), but you shouldn't explain anything that's going on in the game or what the consequences of their choice may be.

If they choose A or B, and there are no legal targets available, ask them to choose another mode. You can't cast Phone a Friend with an illegal mode chosen. Yes, you could just eliminate modes that can't be chosen from the beginning, but what fun is that? If an opponent ends up choosing the mode, they also must choose a legal mode.

"If they don't answer" means you failed to contact anyone or the person you contacted didn't make a choice in a reasonable amount of time.