When writing face-to-face dialogue, I like to give clues as to what the non-POV character is thinking and feeling through their actions. Not all the time, but whenever it feels appropriate. They might be pacing or go completely still. Maybe they're scratching their chin, sipping at a drink, or tugging at a frayed thread.
It's much harder to employ "Show, don't tell" in a phone call. In this particular scene, the character on the other end of the line is reacting to the POV character's news with varying emotions, ranging from cautious and upset to relieved and hopeful. Due to his personality, he's unlikely to voice any of that out loud.
So far I've been using the following techniques:
- raised/lowered voice
- audible sigh/gasp/chuckle
- rushed/chopped speech
- pauses/trailing off
But I'd still like to convey more information, so I've resorted to the POV character commenting (in her head) on what she thinks he (or his voice) sounds like (nervous, hostile, accusatory, hopeful), but that's much closer to telling than I'd like.
How can I show a character's thoughts and emotions if the POV character only hears them?
The story is written entirely in first-person from a single character's viewpoint, but though the secondary character (the one being called) appears less often on page, he's extremely important for the plot.
The main character has previously interacted with the secondary character, but she doesn't know him well. However, I can sort of assume that my audience remembers him from other stories, so hopefully they'll be able to work out what's going through his head as he's receiving the news. (That said, I would prefer not to rely on that too hard, as I myself sometimes read series out of order, and would assume others do the same.)
EDIT: As pointed out in the comments, changing it to a video call is an option. However, I would prefer not to do that because it would greatly reduce the tension of the scene, and I also don't think the main character would trust the other character enough. Still... it's an option I hadn't considered.