I often hear salespeople put on a different voice when speaking to clients.
They have probably been told they need to exude more gravitas and authority. But that doesn't mean putting on a fake voice.
People have to connect with you, and that means being yourself.
You have to be authentic.
There are ways of exuding poise, gravitas and authority which don't involve trying to be someone else.
Slow down, pause more, breathe deeper. Take the time to connect with the person on the other end of the call.
Listen more and respond intelligently based on their unique situation. Have empathy and demonstrate that you care.
Be the very best version of yourself.
Never try to be something you are not. It doesn't work and people see right through it.