Why does my screen go black in 30 seconds during phone calls ???

My screen timeout is set for 10 minutes, but when making a phone call, the screen goes dark in 30 seconds !!! I have a Samsung s9+, which I just got !!! On my Samsung s4, I was able to enable my proximity sensor, and the phone screen would stay on as long as I wanted it to, which is good when dealing with customer service type calls, or if on hold !!! Is it just me ???

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