Samsung support told me only the geek squad at best buy knew how to fix this unacceptably anoying "feature."
After scheduling an "appointment" They had no clue as to how to fix the issue. More of my time wasted. This S9 is not a particulary good phone in general. I am very dissapointed in it. And thanks again Samsung support, for lying to me!
Just picked up a Note 9 - I am on speakerphone 1-2 hours a day. Crazy how there are settings for SO many features, but not this. Just downloaded the Keep screen on app, will see how that works.
i got the dark screen when i am on call. then I came across solution about sensor. I used keypad to key in *#0*# and press the "sensor" to check if my sensor is blocked. It turn out that my sensor is blocked (the test screen was GREEN). and the root cause? my screen protector blocked my sensor even though it's supposed to be clear. Guess the sensor is too sensitive and detected it even though it's transparent. After I removed my screen protector, the issue went away!
Simply pressing the Power key on my S9+ turns the screen back on.
Even if I have that button configured to end the call, it does not end the call once the screen turns off.