Rick has been bananas for a while now. This is just a more "cinematic" way of dealing with it than they did in the comic. In the comic he kept the phone with him, and would have imaginary conversations with Lori when he was alone as a way of dealing with the horrors of life alone, for a long time. I am unsure if this is a good idea or not. In the comic he wasn't overcome with insanity. He "talked" to Lorri on the phone but he was able to pull his crap together when he needed to. The TV Rick hasn't seemed able to consistently hold his crap together at all.