https://www.channels.app/blog/telephone-skills#h1

Despite being one of the most obvious, it is also one of the most (if not the most!) important telephone skills.

Projecting a positive tone over the phone and making the caller feel the emotions that the tone of your voice conveys is what can take you from 0 to 1.

Focus on such emotions as positiveness, happiness, and optimism.

Besides the tone of your voice, it is important that the pace you're speaking in is appropriate. There is no golden rule but the best practice is to speak at a pace of 130 to 150 words per minute. The goal is to sound clear so you won't have to repeat anything you say. This will result in the comfort of your recipient and him clearly understanding your message.

You should also control the pitch of your voice. Here, the balance is the answer.

That's because both sounding too high and too low have bad connotations. You don't want to sound childish but, at the same time, you don't want to sound harsh.

It's important you sound natural, project a positive tone, and speak at a balanced pace.