Why does text notification sound go off during phone conversations?

[AC Question]

I use my phone for business and when in conversation the text notification sound goes off - I hear it in the background and the customer hears my phone breaking up and cannot hear me.

I've priority settings, etc. And nothing is working. I know I can silent it but then I'm constantly checking screen to see if I've received a text

I need to know when I receive texts but silently during phone conversations or not at all during conversation and can retrieve them when my call is complete by checking status on top of phone.