Do me a favor and give me your answer to this:
It should be obvious but having someone use a computer and talk on the phone is much less involved than showing up in person and using an earpiece. Also, I’m not sure how awkward these people normally are, but the in-person faker would be astoundingly obvious.
Yet, based on your previous comment, you think the person will be able to BS their way through a conversation with you about code they didn't write and don't understand. I don't see how you can hold both of those positions simultaneously.
Look, I've done a lot of interviews as the interviewer. This attitude that we have to design processes as if there are five hundred quintillion octillions of googolplexes of novemdecillions of cheating lying "fake coders" for every one qualified person is not rooted in reality, nor is the level of paranoia you're displaying. There are perfectly reasonable processes you can use which will catch a cheater if you actually get one. But designing a process entirely around the assumption that everyone is a cheater trying to lie their way into your company is just not useful.