By locally, I assume you mean running a model on the iPhone itself but if you just mean that you have something already serving AI models locally that you want to interact with on your iPhone then there's a few options out there where you just need a web browser to have voice calls with the model. I'm familiar with Open WebUI as an example.

Not too familiar with running models ON iPhones though. That might be a tougher nut to crack but I know there's folks who have gotten AI models running on Android so I wouldn't be surprised if there's something out there for iPhones too.