Google has that, but I'm not sure if it's on-phone.
I'd wager someone could write an app to do this.
I would probably pay $50 for an on-phone version of Lenny; basically a voice-based chat-bot that keeps spammers occupied, without having to conference another number in.
( https://www.vice.com/en_us/article/d3b7na/the-story-of-lenny... )
I use it for every number I don't know, and so far it's been 100% successful (in the sense that, afaik, no one who I wanted to hear from has hung up on Google Assistant).
You can set the spam calls to be answered with selected funny time-wasting recordings, but since that would be embarrassing if I get a call from a professional contact, I set them to be answered with a plain fax tone.
Now I am back to being able to pick up all calls that ring.
(My opinions are my own, not necessarily those of my employer.)
What I want, though, is an interactive bot, running on my phone, that will eat up telemarketer's time by pretending to be a real person, and responding to them in such a way as to keep them on the line for as long as possible.
I want to pick up a call from a scumbag, tell them, "hang on, let me get my dad", and press the "fuck you" button - which puts a fake doddering old man on the line for them to talk to instantly, without any more intervention required from me.