In a scene where Nelly is in the snooker hall whilst on the phone to Claire, he asks her to "keep it down". When the camera is on Claire, she lowers the phone to her stomach showing that the screen still has the 'decline' and 'accept' button's still on meaning she hasn't yet accepted the call.
In a scene where Nelly is on the phone in the snooker room to Claire, she gets some bad news and lowers the phone she's using. On the screen when she lowers it, you can see the 'decline' and 'answer' buttons showing that she had not yet accepted the call.