Can not get iPhone to make absolutely no noise

Hello I am using an iPhone 11. I am using software 17.4

I am trying to use my phone to record conversations and testimony in court but, in that environment, my iPhone can make absolutely no sounds whatsoever without incurring the great wrath of the judge.

I have been to my iPhone store four times to consult on my problem. My problem is that I cannot find a setting that allows me to use the iPhone to record or, perhaps, listen to audio, while at the same time making absolutely no sounds. no phone calls, no notifications, no alarms, no sound at all. Period.

Similarly , I also have my iPhone settings set for absolutely no sounds at night. I just had the "be silent" setting on and, unbelievably, I just got the "text coming in" sound.

As I said previously, I have been to the Apple Store four times seeking an answer to the question of how you can keep your phone operational but at the same time have your phone make absolutely no sounds whatsoever. I have steadfastly followed the instructions given to me on those four occasions by the Apple Store workers, but I still keep getting sounds when I have followed instructions on how to turn all sound off.

Is there something wrong with my phone or am I getting bad information on how to do what it is I am trying to do.

I thank you for your time, attention and any help that you can give me with this persistent problem.