There could be a variety of reasons why you're experiencing trouble with the proximity sensor. Please take a look at some of the steps below and try these in order, moving on to the next if the symptoms persists. This should resolve this.
2.) Clear the phone app cache (Settings>Apps>Phone>Storage>Clear Cache)
3.) Clean the proximity Sensor and check for Damages - Over time the proximity sensor on your device can accumulate dirt and grime, you should be able to clean this off with a soft dry microfiber cloth. The sensor is normally located at the top of the screen near the ear speaker.
4.) Screen Protector: Are you utilizing a third party screen protector? Some screen protectors may block the proximity sensor from working properly. Try removing the screen protector and see if the symptom persists, if they do not, this would indicate the protector is the cause.
5.) The screen could be lighting up if accidental touches are taking place during calls. We recommend trying the accidental touch protection setting and turn this on. (Settings>Display>Enable Accidental touch protection)
6.) If none of the steps above helped with this - it's recommend to have a technician take a look to diagnosis the symptoms to find the root cause. You can set up service by visiting: HTTP://www.samsung.com/us/support/service
