iPhone 6s has gained popularity due to its sensors especially proximity sensor which is by far most efficient in this model of iPhone. The sensor restricts the phone to make accidental taps during a call by detecting when phone is held near ear. The sensor is present right at the back of speaker on top of LCD screen. Although, Apple Company has put a lot of effort in making it functional flawlessly 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.