You could well be right that porting the phone number from a Voda FTTP connection could terminate the overall service.
On my OpenReach Voda FTTP I effectively had three separate services with three different reference numbers.... The broadband and it's account number which was a ten digit number, the phone line and it used the phone number of the landline as the account number, and the backup 4G SIM card which used it's SIM number as the account number. All account numbers seemed to be treated equally, entering one always brought up all three services jointly in the Voda portal. This doesn't probably help either way to know if you can port the landline phone number without causing the entire contract to cease but the fact that it appears to be built as three separate yet joint/bundled services might give some hope.