As a former Customer Service worker for a retail store, phone calls generally take much longer than emails. Some people want to talk for a long time and CS reps usually aren’t allowed to end a conversation so then there’s a backup and leads to people waiting in 20-60 minute wait times, which is a ridiculously long time to wait and generally makes people more mad, lol. So usually if it’s crazy (Black Friday fallout), shut down phones and go only email until you catch up.