iPhone 6s plus is gaining popularity due to its sensors especially proximity sensor which is highly efficient in this model of iPhone. The sensor detects and skips the accidental touch taps during a call when the phone is held near ear. The sensor is located right at the back of speaker on top of LCD screen. Although Apple has put a lot of effort in making it functional flawless yet there is a possibility of the damage to the proximity sensor. Especially if you had a contact with water or live in a moist area or had greasy hands frequently when using your iPhone 6s plus, the sensor might get faulty and needs a replacement or repair.