This PCB converts the two screw terminals on a BT / Vanderhoff Test Telephone 286A to an RJ11 and RJ45 socket - the idea being you can then use additional adapters like an RJ45 to BT "Master". I have ...

The console port offers a RS232 interface using a RJ11 or RJ45 connector. The voltage levels are not TTL-compatible. A RS232 transceiver must be placed between the Batteries and the ESPHome device.