Source: Juli Phone telephone answering machine, about 1970 | Science Museum Group Collection

Closer look

Juli phone with tapes and remote control

Telephone answering machines did not become widespread until the 1960s. At that time they were quite bulky machines and usually to be found only in offices. The Juli Phone, made in Japan in about 1970, is typical in its size and is solidly constructed. A small ‘activator transmitter’ was included which could be carried around by the owner and used to play over incoming messages on a telephone remote from the machine, for example at the owner’s home.

EDIT: I suspect the metallic piece would work similar to the ANSAFONE. See this this video from THIS MUSEUM IS (NOT) OBSOLETE (link to working demo at 14:43):

But intead of lifting the phone, it would just press/unpress the button.

Something like this