It's an old version of a (pre-plug-in) faceplate
that would accept one end of the cable from a dial telephone.
The centre 'nipple' is removable and allows the moulded end of an old telephone leade to be fixed in place.
Behind the plate will be a connector block (which is currently used to connect the LJ2/1A below), but would have been used to terminate the telephone lead, in a similar manner to this
You* could remove the LJ2/1A and old face plate and replace with a flush-fitting NTE5 to make it look neater.
* Carried out by a suitable authorised/competant person.
Eats shoots and leaves.