This issue is attributed to the phone's proximity sensor. On the POCO C61, the proximity sensor is integrated with the Touch Panel (TP) technology. This sensor is designed to detect when the upper third of the touch panel is covered, which happens when you hold the phone close to your ear. If the sensor is not working as expected, it is due to insufficient coverage of this area or a misalignment in the sensor's response.
To ensure the sensor activates properly, make sure to hold the phone as close to your face as possible during a call. This reduces the distance between the sensor and your ear, helping the phone recognize that it should turn off the screen. If the problem persists, please check if there is any obstruction or issue with the sensor's calibration.