I thought this was called The Spectator but a search reveals nothing,here is effect.
A random phone number is generated ,this is then called by spectator,person on other end of line with no prompting from performer reveals chosen card/word/object! I think it won trick of the year or something not long ago.

Ah it's The Stranger I found out now.

It could also be Diverter by Marc Kerstein! It’s also an App with the same effect!

Both Stranger and Diverter do similar things, but IMO the Stranger is more fleshed out and has way more options/integrations. the app has become a powerhouse! also it's available on both iOS and android, where Diverter is iOS only I believe.