You answer the phone and your dog starts barking at you. Your attention has shifted to a device, but from your dog's point of view you are still in the room and talking. If a bark has made you throw a toy or hand over a snack before, they may also have learned that phone calls lead to a little game.
Check the basics first. Does your dog need a toilet break, water, or movement? Is a sound outside the window setting them off at the same time? A sudden change or barking paired with distress needs more than a phone-call trick.
Practice before you need silence
Lift the phone to your ear, say a word, put it down, and reward your dog for staying relaxed. Repeat in a quiet moment. Add a few more words and a little more time across short sessions. If barking starts, make the next practice shorter. Teach a comfortable mat or a safe food puzzle as an alternative activity, reward your dog for using it before a call becomes noisy.
For a planned call, give your dog a chance to move and toilet beforehand. Set up their mat or suitable enrichment before dialing. During the call, quietly reward relaxed behavior when you can, then return your attention afterward. Do not make a habit of handing out something exciting only when barking begins.
If your dog gets worried when you are on a video call because people or sounds appear on the screen, address that part separately at low volume. The goal is not a dog who understands your calendar. It is a dog who knows what pleasant, predictable thing happens while you are talking. For more on setting up small habits you can repeat, see the everyday training-routines guide, start the quiet activity before the call becomes difficult
Sources: American Kennel Club: Why Do Dogs Bark When You're on the Phone?. ASPCA: Barking.