The only way to remove a phone number from your AT&T phone bill is to not call the number. There really is no other way.
Every call that is made from the phone or received by the phone that logged call time is registered on the bill.
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Otherwise you can't
But you can prevent them from showing up in the future by... Not calling them ;) lol
If it is showing the incoming calls to, then you can ask that person to stop calling your number.