Nuki Opener + 2 wire telephone line

I have a standard UK landline (two-wire RJ11 BT Socket) that gets called when my intercom is used and if I press the hash key (#) then the door opens. I only have this landline for use with the intercom so I want to connect it to the Nuki Opener - the intercom of the building itself is made by “Telguard” but I just have a basic landline phone attached to a Virgin Media Router that gets called.

I have tried connecting a basic setup
Bus + (RJ11 green) → Nuki RED
Bus - (RJ11 red) → Nuki BLACK

and used a generic bus setup - but the phone does not ring if the Nuki Opener is wired in.
I can still hear the dial tone and it can make outgoing calls - it just won’t ring when it’s called.

Does anyone have any advice when working with an actual telephone system?