Welcome to this user forum.
Nobody has reported this issue before. Does it show as a reduction in the number of signal bars on the mobile phone when the home hub is turned on?
What happens if you turn off the wifi on the mobile phone, can you make mobile calls then?
Are you on normal broadband or BT Infinity?
If you are on BT Infinity, are you using the home hub in conjunction with a separate Openreach modem?
That sounds like a faulty home hub, as it should not radiate interference in the mobile phone band.
Ther could be a parasitic oscillation taking place inside.
I would ask for a replacement.