If I do not know a number, or no name attached to it I know.
I always answer,
"What".
The voice Reconication software, associated with robot calls,
do not recognize the word, 'what'.
If a voice starts talking, I will say,
'What's 2 + 2', If I get no answer, it's , 'Robo" !
If it is a live person,
(rarely these days),
they say, 'What' ?
At that point I determine if they are legit.
If not, well they get a few commits.
(Just for EDS)