That's not the issue. LLMs are not trained on whatever crap you can scrape from users text messages or emails. That is relatively useless for training.
If you believe the memes, Siri is already quite capable of searching Google for you.
How is that a meme? It casually searches Google and summarizes the result when required. Siri runs locally on iOS and needs to use a search engine to lookup information.
https://www.theverge.com/2021/6/7/22522993/apple-siri-on-dev...
"They're failing because they're soooo privacy conscious"