I've declared phone call bankruptcy yesterday and decided to do exactly that. But at least on the iPhone, I couldn't find a way without affecting notifications (by putting it on Do Not Disturb).

I believe a call from anyone worth answering will probably result in a voicemail, and I know that robocalls leave voicemail, so I know it's not a perfect plan. But I am at a point where I would rather just ignore "phone" functionality on my iPhone than to put up with the huge daily distraction of robocalls.