My son and I have the same issue. I've done a lot of testing and you'll find this hard to believe. I encourage you to do some tests of your own and post your results so Apple Engineers can figure this out.
Recap: My wife, son, and I all have the same
phones. iPhone 11 Pro Max.
I have the Otterbox Defender. It has a hard clam shell and a rubber skin that goes over the clam shell.
My son has same phone but Otterbox Symmetry.
My wife has the GEAR4 Crystal Palace case.
Scenario 1:
Wife on porch with phone.
I call her from kitchen with full case on my phone.
I start counting out loud into my phone and she starts talking in the middle of it. This simulates the person you called trying to talk at the same time as you or background noise which I found causes the issue as well.
She said my voice cut out while she was talking at the same time.
Scenario 2:
Wife on porch with phone.
I call her from kitchen without a case on my phone.
I start counting and she starts talking in the middle of it.
She said no problems.
Scenario 3:
Wife on porch with phone.
I call her from kitchen with clam shell on phone but not the rubber skin of the case.
I start counting and she starts talking in the middle of it.
She said no problems.
Scenario 4: (This was just a gee whiz test that makes you say what the heck.)
Wife on porch with phone.
I call her from kitchen with phone in the rubber skin of the case but not the clam shell.
I start counting and she starts talking in the middle of it.
She said my voice cut out.
Scenario 5:
Repeated scenario 1 but switched phones to see if wife’s phone would fail with my case on it.
Hers cut out the same way.
Scenario 6:
We repeated the same tests with his case on and off but using FaceTime.
With his case on, he cut out when I talked while he was counting.
With his case off, I could hear him fine the entire time.
The issues appear to occur when using speaker phones in certain cases. How is this possible? Without knowing why, we customers are hit and miss on phone cases for iPhones. This really needs to be explained.
Hope these tests and results help. Now I need to know what case I ca n use to help protect the phone better.