mmmh, I've always found hard to explain that to my too... this because in phone you have a "free" from, so it could be a customer/internal/extemporaneal request too, in the other case you just have a "queue selection" as from.
Phone-Ticket is for incoming issues, like phonecalls or something you were told during lunchtime or kinds of that.
Email-Ticket is for outgoing issues, like "Dear external Service Provider, our plants are dry" or "Dear Customers, tomorrow we will have slow internet connection for about one hour."