Do what you need to do. Avoid kitsch.
If it’s a normal two-party phone conversation, I’d expect it to be written normally in natural dialog. For a multi-party conversation, it gets tricky. I’d say that the perspective is very important in this case… first-person, third-person…?
Stylistically, changing fonts in a story is something that I look at like this: Don’t do it unless it works. And what that means, basically, is that you shouldn’t do it unless you’re sure you can pull it off… and are certain that it adds to the story.
If I was writing a scene like that in third-person (I don’t like first-person), it might perhaps look something like this:
Tellia peeked around the corner of the ancient stone cottage, then snapped her head back and bared her teeth. The Charan skirmishers advancing down the wide avenue were methodically clearing the buildings they passed, closing on the little alcove that sheltered her and her new charge.
She slunk over to the little coyote and touched his chin with her finger, lifting his head.
“We must go, child. I’m sorry. She’s…at peace,” Tellia murmured, ears angled backwards as she listened to the shouts and scuffles of the enemy.
The coyote twisted his head away, expression twisted up in a tearful denial. He fell to his knees, shaking the curled body that Tellia could only assume was his mother’s.
“I can’t carry you,” Tellia whispered urgently, taking his paw. “But you must come.”
“Aleph?” The voice in her ear was distorted with radio interference. “Why aren’t you moving?”
Tellia grimaced, squeezing her fingers together to activate her transmitter. “Little snag. Moving now. Come on, lad,” She growled.
The coyote tried to pull away, but Tellia squeezed softly, tugging him back to his feet.
“Those rattlers are at your 140, two hundred meters and closing.”
“Oh great,” she grumbled. Backing toward the little alley, she tugged the youngster with her and unslung her carbine. He resisted for a moment, then to her relief acceded with only another little glance back.
“Moving,” she transmitted, duck-walking backwards until she was able to release the coyote’s paw, pushing him behind her. She glanced down. “Speak standard?”
“Yes,” he whispered, voice tiny and subdued.
“Ok. I’m going to walk backwards. Stay right behind me, ok?”
She perked her ears at voices from down the street. From the few words of Charan she knew, she could tell that the skirmishers had found the coyote’s body. Shepherding the youngster with her paw, she backed into another alley, this one full of trash and debris.
“Base, Aleph,” she subvocalized. “I need an outlet or some cover.”
“Follow that alley, then dogleg west two streets down until you come to a park. Goshen’s snipers can cover you through the park.”
Light, booted footsteps from the street caught her attention, and she gestured for the coyote to move more quickly, angling for the shadow of a dumpster.
Some inbuilt instinct taught him to move quietly and stealthily; even his breathing was almost silent, she noted with approval. Growing bolder for that fact, she continued to move, in and out of cover, as the line of soldiers began to pass the deserted storefronts a scarce hundred meters away. One street, two streets down and she exited onto a frighteningly broad road, pulling the youngster around the corner and into the mouth of an old cafe. A quick glance through the windows showed it devoid of occupants, though its polished, well-kept equipment was still on and ready to serve customers who would never return.
She glanced down at the coyote, resting her paw on his shoulder. “What’s your name, kid?”
“M-morai,” he said.
“Aleph, you can’t stop. You’ve gotta cross there. Now!” Her dispatcher’s voice was strained. “Those rattlers are about to cross.”
She grimaced, compulsively checking to make sure she had a round chambered. “Roger. Ok, Morai, I’m Tellia, but you can call me Telly. We need to run now. Can you run fast?”
He nodded, eyes wide. She knelt low, then pointed across to the alley one street down.
“Run over there, as fast as you can, ok? I’m right behind… you.”
Tellia blinked as he took off before she’d even finished. With a surreptitious glance in either direction, she followed at a sprint.
Two crackling hisses ripped by her head mid-street, followed by a distant crack. She nearly tripped over her boots, but caught her balance; resisting the foolish instinct to return fire, she instead jinked and increased the length of her strides. The coyote was indeed a quick runner, and she didn’t catch up to him until she was nearly across. She snatched him up mid-stride, making the cover of the buildings just before another burst of fire slammed into the facades of the little shops behind her.
She panted, glancing back over her shoulder. She turned back forward, but her eyes widened—a section of building had collapsed across the alley, and the way forward was blocked.
“Dammit,” she transmitted. “Base, this is a dead-end!”
There was no reply; excited shouting in the street behind her drove her to run to the debris, trying to find a way to climb it.
A tug on her paw had to be repeated twice before she glanced down.
“Here. This way,” the coyote’s voice was urgent but compelling, and she followed him across the alley to a utility door.
“It’s locked,” she snapped. With a glance back at the mouth of the alley, she groped for a grenade, mouth dry.
They wouldn’t take her alive.
I suppose that’s not really as dense as the scene you’re describing. I dunno if there is a right answer, though. Italics, to me, suggest too much of a removal from the present and verbal. I like them for deeper, more in-mind things, like telepathy or mental dialog. Messages and textual communication can be set off in italics, or with indents and spacing, but as someone else says, clarity is king. Use what works.
I don’t think a phone call is ‘special’ enough for special formatting. Perhaps it’s what’s around the phone dialog or the verbal dialog that needs to be revised for clarity. But even then, one person’s clarity is another’s kitsch. Some people will have diametrically-opposed viewpoints on a technique. In the end, in my view, look at it like this—if someone has trouble with it, multiple people might, so it wouldn’t hurt to give it another glance for clarity. In the end, though, playing around with it, trying new things, and seeing what reads best to you is probably best.
As far as the italics for emphasis, I like it too. Sparingly. And generally only in dialog. Italics can provide emphasis in dialog that substitutes for tone of voice, and make dialog sound more natural. Misused, though, they can instantly transform good dialog into stilted dialog. It’s interesting to re-read old stories of mine were I’d used italics in dialog to convey accent—now and again, I’ll come across a line of dialog that I just can’t re-capture the voice of, and the italics are just odd.
Sometimes they work in close-in perspective, as well.
I wouldn’t italicize onomatopoeia, but foreign words and phrases that haven’t been accepted into English generally must be italicized. There are lots of other little oddities that are italicized by convention, as well, such as ship names.
In the end, though, while you can incorporate others’ tricks into your writing, in the end if you depart from your voice it WILL most likely stand out.