i imagine they will ask the phone provider 'was it being used?'
Surely they would check the phone records routinely to see if they were were on the phone?
Depending on the area (built up vs countryside) wouldn't they be able to show that the phone was moving whilst in use ... Mr Summerdays knows more about this sort of thing though he is now no-longer in that industry - but he had to provide evidence as to where a phone call was made from for the courts before now.
And I thought that your mind could still be on that call in the moments after the call finished so that you are still continuing to be distracted by it.