It's extremely unlikely you will be able to retain your analogue copper phone service if you move to FTTP.
You will almost certainly be moved to Digital Voice. You will have to bite the bullet at some point in any case as the PSTN is due to be switched off by 2025
The way the home voice service is being delivered to you is changing for all anyway. Have a look at the following resources to understand what you need to do to be prepared for the move to Internet based voice services (VoIP/Digital Voice):
Lots more helpful resources on why this change is happening and what to do: https://landlinesgo.digital/resources/