I think you might've done this, but I don't remember. Anyways, my question is how would you write a phone call between two people but the point of view character can only hear one of the two? (Not sure if that's clear enough) so, a person is in the room wi

By writing out the dialogue of the person speaking and using their responses (both verbal and physical cues) to indicate what’s being said on the other side. 

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“Hold on. I have to get this.” Stacey picked up the phone. “Hey, Jeremiah,” she said, crossing her arms under her chest. 

Adam dropped down on the sofa with a sigh. Once again, her brother was getting in the middle of things. Would they ever get to talk about what had happened? He watched Stacey pace across the room, freezing at the doorway. 

“Wait. What? Slow down and tell me what happened.” Her face darkened as she listened. Adam could only imagine what trouble Jer had gotten into this time. For the next couple of minutes, she didn’t respond, but her expression continued to grow increasingly bleak. 

“Okay. Listen,” she finally managed. “Just stay there. Don’t do anything. I’ll be there in just a minute.” Then she dropped the phone on the counter and leaned back against the wall, eyes closed. 

“I guess I should go then–” Adam started, but she put her hand up. 

“No. Don’t. Please - come with me. I need your help.”