People were vastly more careful about interrupting you via phone, in my experience. The careless way people interrupt on group chat is an extension of the general way people tend to dehumanize others online.
> I think you just have to clearly communicate that the group chat, in your case, doesn't benefit the working relationship.
Yes, I've not only said that, but proved it (by being extraordinarily productive during a 2-week "chat free" trial period). But the clients I deal with want me to be on chat, I'm guessing for the same reason that they'd really rather I work in their office. So the managers can monitor the hours I'm "clocked in" (nevermind what I actually accomplish during that time).
Basically, chat lets employers monitor their workers (even contract workers) in the same way that they monitor their workers in the office, by observing "butts in chairs".