Well, unless I’m missing something, or the Sky hub behaves differently to BT’s. You may find you’ll have the same problem in that the Sky hub also has an in built DECT base station and may interfere with your existing base station. If it doesn’t, then the problem should go away.
Just so you know, both services - SKY and BT’s Digital Voice - use VoIP (Voice over IP)
In my case I will have to re locate my hub in any case to make it easier to connect to the ONT when I go full- fibre.
Just curious and perhaps useful to others, did you try moving the Hub and your phone’s base station away from each to see if the issue went away?