A. 1. Check if the proximity sensor is obstructed. Clean the area around the front camera and sensor. 2. Go to Settings > Sound > Advanced settings and ensure that 'Speaker' is not set as the default audio output during calls. 3. Restart your phone to refresh the settings.

B. 1. Test the phone's proximity sensor by making a call and covering the top of the phone with your hand. If the screen does not turn off, the sensor may be malfunctioning. 2. If the sensor is faulty, consider using a screen timeout app to manually control the screen during calls.