It's not a violation. I went over this in VERY much detail with my therapist and this is what she told me. Phone is not a method of secure communication and ts run the risk if they use this method to keep in touch with clients. If they choose to use phone, the client can say whatever they want, and they are supposed to be informed that anything they say isn't necessarily confidential. It's what the t says back to the client that would be an ethical violation. Technically, if they address anything over phone that isn't about scheduling, its a breach of boundaries.