Define "almost everyone," please - sorry, but that's not been my experience. Several clients and friends (we run a development firm) I've tried to converse with who own iPhone 11 Pro, I hear my side of the conversation booming back at me. Its extremely disconcerting, enough to be forced off the call.
It happens if the phone is sitting on a surface, if it is nestled inside one of several (Apple) cases, and if the person is holding the phone in a "normal" fashion, (presumably with the base of the phone in proximity to the palm of the hand). The only solution I've been able to recommend is turning the phone upside down, speakers pointed to the sky, and converse as if the phone were a microphone. Or, wearing plugged in earphones the problem disappears.
I would call that a major hardware design flaw in a $1,000.00 mobile device, and until I learn that Apple has fixed it, my upgrade plans (from iPhone 8) are on hold.