Not that I'm aware of, my logic is pretty good, remeraber she went to the store before the explosion, leaving at that point is fine, but leaving after the explosion is risking Reiji coming back and her not being there so going to a pay phone was out of the question, Cal was manipulated by Scythe, remeraber he's very good at doing that to people, I do however agree with you that Reiji could of done more to find out if Cal was really in the flat.
Episode 20 was pretty good, not sure what Cal is intending on doing, I guess from her view point Reiji left her for somebody else, I'm sure Scythe would of told her that too, Cal does have the advantage though, she now has massive guns