My initial thought (until I noticed the diameter of the cable) was that it was a LV
* supply for, say a street light. No, definitely not.
But you must take first prize as, yes, that is a telephony cable. I can see bits of old salt-glazed earthenware duct. However do I wonder about the thick "up-sticky" cable end. Possibly lead sheathed? (I won't as you to put your finger on the end to see if it still connected somewhere . . .
)
* Apparently the standard domestic mains voltage is classified as low voltage, hence LV, above.