on the phone so dont utter a word is correct way of using utter?

The sentence "on the phone so dont utter a word" is grammatically correct, but it's a bit awkward. Here's why:

* "Utter" implies speaking, which is already implied by being on the phone.

* "Don't" should be "don't" with an apostrophe.

Here are some better ways to say it:

* "I'm on the phone, so don't say anything."

* "I'm on the phone, so please be quiet."

* "I'm on the phone, so hold your thoughts for a moment."

These options are clearer and more natural.