ORBI 42 RBR350, D-Link DSL-X1852E connected to VOIP phone. Need ORBI to boost Wi-Fi to living area.

Hi, Sorry for slowness in response. Have to work around others' needs with either access to internet or access to phone.

I think you have provided the information I need. The last hurdle - I think ISP has special arrangement with fibre support company as to what is coming through the ONT box.
I now need to contact them to see if it is possible to change back to same setting at our address as we had in the past with all our other ISPs. (not us changing them, but other companies amalgamating or being bought out by bigger fish)..

Once I am sure, I can set the ORBIs up as your per your solutions - YouTube excellent, restart everything, plug in the phone and hopefully be fully functional again.

I have learned a lot from you regardless. Thank you!