So was 'Lori's' call a wake up slap to Rick, or just more proof he's lost it.

I think it was more about the guilt he was feeling regarding how he treated her since finding out about her and Shane. He never got to fix the relationship and tell her that he still loved her. So, he was basically having the talk that he wanted to eventually have. The phone was more for the viewer rather than having him babbling in an open room or having an inner monologue.