OK, not been on here for a few days......
That
is a jointing post. It is a DP (distribution point) in the same way as the box on the top of a pole is, or the main box in a block of flats.
Inside there will be a main feed cable, most commonly a 20 pair one, and then the ends of the local cables that go to the individual houses nearby.
There is currently a project underway to replace the lids for these with ones made of plastic, this is stop dissuade the criminal fraternity from half-inching the lids.
It is common for them to get 're-made' back in to the adjacent footway box, as you can imagine, several decades spent at dog pee height makes them far from ideal housings for a telephone joint.
I would guess that the area where the OP was walking had houses built between 1965 and 1975.......