If the current Openreach ‘line’ is underground , if it’s ducted the same duct is used to bring in the fibre cable to your house wall , if it’s DIG ( direct in ground ) then a small excavation is needed from the footpath to your house wall , and possibly from the footpath to a footway jointbox that houses the fibre ‘connector’ …this work done by Openreach or a contractor working on behalf of them.
The property gets a block fitted ( a CSP ) where the external cable exits the ground and another internal cable runs from the block to the ONT , which is a powered device so needs to be near a power outlet, the ONT can be where you want it , within reason , it doesn’t have to be near the existing master phone socket , unless that’s what you want , the router connects to the ONT .
If you want telephony ( its optional you don’t need to take a phone service ) as with all new provision it will be via the broadband service , the phone plugs into the router so a power outage will stop the phone working , for those without a mobile and sufficiently concerned, there are ways to keep the service up by using a battery back up / uninterruptible power supply
