The telephone is hard because the face is missing.

On a call you lose every visual clue at once, and nobody warned you that you were relying on them.

When you talk to someone in a room, you are not only listening. You are watching their mouth, reading their eyebrows, catching the small nod that tells you they are about to finish. You use all of it without noticing. On a phone call every one of those signals disappears in a single step, and what is left is a thin, compressed voice with the low tones stripped out. Then people speak faster on the phone than they do face to face, because they treat calls as errands to be finished. So the situation is harder and quicker at the same time, and you are meant to manage it without preparation.

Knowing this changes what you do about it. The answer is not more vocabulary. It is more control of the call. Write the two or three things you need before you dial, in the order you want them. Say who you are and what you want in your first sentence, because that sets the topic and a known topic makes strange words guessable. Keep a pen moving on paper as they speak. And use the strongest phone sentence there is: sorry, the line is not very clear, could you say that again more slowly. It is polite, it is ordinary, and it buys you a whole second attempt.

Give yourself the easy calls too. Ring to ask an opening time when you already know the answer. Ring to confirm a booking you have in writing. There is no risk in these, so your body stays calm, and calm is most of the skill. The fear of the phone is built from a small number of bad calls, and it comes apart the same way, one ordinary call at a time.