Not a phone jack. Around here anyway, back then the phone company itself did the internal wiring, they used biscuit jacks mounted on the baseboard and would have never have mounted something in the middle of the floor like that, especially with a '3 screw head triangulation'.
The wire colors are also wrong for Bell wire, the primary pair is red and green, secondary pair would have been black and yellow. And they would have been smaller than 16 gauge.
Sewag, maybe a footswitch to buzz somebody in the front door. Maybe a buzzer... The location and the way it is mounted tell me it is a grandpa special and nothing that was original to the house.