You've obviously got 'Freesat from Sky' (which, confusingly, isn't the same thing as 'Freesat'). That means that you're getting lots of extra channels when compared to terrestrial Freeview services (although you probably don't most of them anyway) but losing out on some popular channels (such as Dave, Yesterday and Drama) which are only available free of charge via Freeview.
However, to answer your question, this is taken from the Freesat from Sky terms & conditions:
"Q: Do I have to connect my Box to a phone line?
A: No. However, as part of a standard installation we will try to connect your Box to a working telephone line to enable you to make full use of the interactive services available on the digital satellite platform. We will do this unless you ask us not to, or an appropriate socket is not available, or the Box cannot be connected for another reason. In connecting the Box to the socket we will use the nearest available socket and any cabling will be clipped to the relevant skirting."
So you don't have to retain the telephone connection to your Sky box.