Contact Hyperoptic and order a broadband service with a connection speed that suits your needs. If their ONT is missing, then an engineer visit will be required.
In many flats Hyperoptic don’t use ONT, but a RJ45 ethernet connection, as they have a business point to point connection elsewhere in the building and switches to share it between properties. It is possible they can sell using other wholesale networks now though.
Hyperoptic can optionally supply voice via their router, HyperHub:
https://www.hyperoptic.com/faq/posts/how-does-hypero...
Given it sounds like a BT port on the back, you could plug in any DECT base station if you need cordless. Then less expense.
You are not obliged to take a VoIP service with a fibre service, falling back on just your mobile for voice calls. I personally would not make that choice.
Millions have, including myself. But I do (strangely) have three mobile phones on different networks.
Remember that during a power failure you lose your phone service with wireless phones but that issue can be overcome with UPS hardware which will escalate in price as you seek longer periods of service.
My broadband is with Virgin Media, in a power cut the cabinets in the street go off. Doesn’t matter what UPS I use.
Picking up on the points made in response to my earlier posting:
* I doubt that for an MDU new service, it can be totally an DIY affair.
* The inbuilt ATA of the ISP supplied router for a VoIP service is often locked to that ISPs offering. Not ideal, but you can of course use your existing PSTN hardware connected to the router. To use an alternative VoIP provider then a separate ATA would be required or digital voice hardware. However, Joe Public tends to fall back on using their mobile phone only; the jury's out on that being a wise choice.
* Many of use have to use WiFi calling as the public service is poor or non existent, so a loss of the internet means you are totally cut off from the outside world.
* I personally think it is totally unacceptable for any roadside telecoms cabinet to go down immediately following a power loss. Those that don't become congested with the sudden increase of traffic. Fibre to the home should bypass that issue, so having a UPS in place is worthwhile but an expensive luxury.