This is a VERY hard question for him to answer.
It ought to be easy. Here's the single phone I used in the WH.
But since he was probably using disposable phones, of which there is no record and which he will have tried to destroy, as well as other people's phones, he is going to want to lie.
But he'll be scared the committee has evidence and maybe even some of the phones.
So what will he do? My guess is he'll refer to WH records and say that otherwise he has no memory of which phones he used when.