It’s odd that people, including typically very conscientious people, often answer cell phone calls while in the midst of conversation with an actual person. I’ve seen this multiple times. What’s strange is on several occasions the other person’s cell phone quietly vibrates and the person picks up the call with only subtle indication, as though I’m supposed to know that the phone vibrated in the person’s pocket.
My advice is this. If you’re going to answer a cell phone call in the middle of your conversation, make it very obvious that you have to take the call, apologize for the interruption, and make it obvious that you’ll return to the conversation immediately after the call. Else it’s just awkward for the other party.