At least on iPhones, when you’re using speakerphone, the mic used is at the top of the phone, right next to the ear piece so you can use the screen and talk into it at a natural angle. Pretty sure most Android phones are the same. Most people don’t know how many mics are on their phones and don’t know how they work at all.
I often hold my phone like that, but not talking in public. I think it’s an unconscious “this works best” thing we’ve figured out.
At least on iPhones, when you’re using speakerphone, the mic used is at the top of the phone, right next to the ear piece so you can use the screen and talk into it at a natural angle. Pretty sure most Android phones are the same. Most people don’t know how many mics are on their phones and don’t know how they work at all.