Phone conversations where you show both sides of the conversation are fairly easy—you just handle them like regular dialog for the most part. But what about one-sided convos?
A convention I really like is to use an ellipsis to indicate the unheard speaker’s dialog.
“Hey, girl! It’s Anne. … Nothing much, what are you up to? … You wanna grab lunch at Catfish Charlie’s? … Okay, see ya then!”
In this case, you have full punctuation, but a space between each snippet of conversation (Dialog space ellipsis space dialog). It gives the reader a real sense of how the conversation is flowing, lessens confusion, and makes it easier for readers to follow the phone call.
Win / win / win.