I think it needs a special AI accelerator chip which is first coming in the Pixel 4 phones.

I don't care if it takes a few minutes to process the data... I just want the app

so the chances of it on the iPhone are slim then :(

Apple would more likely to remove every single feature from iPhone before allowing something like that on phone calls.

You mean before allowing someone else to do it? You almost sound like you think apple cares about privacy any more than it serves their financial interests at the moment.

I thought apple already had ML functions like this for facial unlock.

They also used to provide transcripts of voicemail done locally on the phone (although it was not great accuracy)

They also use ML for "Hey Siri" and the face detection in the photos app.

Edit: Here is the article where apple talks about how "Hey Siri" works: https://machinelearning.apple.com/2017/10/01/hey-siri.html