iPhone 5c proximity sensor problem

Hmm... she uses simple silicon case, so it would be strange if it interfered with the sensor. But it was off when the phone was at the service, so we will test the phone without the case for the next few days. Thanks for the suggestion.

And the general problem with the "hand" test in our case is that the sensor works during this test even with the case on. I mean the proximity sensor always reacts when I place my hand over the phone, but not always during the normal usage of the phone (I guest that is why the service claims that the sensor is ok).

Thank you all for your suggestions. It seems that I have found the reason of this behaviour. It was not the case nor the hair. My wife simply was to fast 🙂. I mean, she answered the call (slided her finger on the screen) and then very fast put the phone to her ear. It seems that she was doing it so fast, that the phone didn't have time to switch to call mode and thus did not deactivate the proximity sensor. It is strange, but I asked her to wait for about one second before she put the phone to her ear (after answering the call), and there was no single case of the problem since then. I figured it out when I noticed that the problem was occurring at the beginning of the call only.