When the upgrade was requested to full fibre, did you specify that you wanted Digital Voice. If not you probably can't get it added subsequently (depends on whose fibre network it is).
If you do have DV and you have the hub 2, you simply connect a landline phone to the phone port on the rear.
If you have the Eero router, then you need a Grandstream ATA to go between the phone & the spare Ethernet port on the Eero.
