Android wins this one and it is not close. The reason is boring and practical: you can actually get model files onto the device. Download a GGUF in the browser, point an app at it, done. - PocketPal AI is the first install: loads GGUF models directly, chats offline once the model is on the device, free to start. - The honest limit: phones run small models, typically 1B to 8B quantized. Writing, summarizing, brainstorming, chat. Not datacenter reasoning. - The other pattern: heavy model at home on Ollama or LM Studio, phone as the window. Same privacy story, bigger models, one more machine. - The model matters more than the app. Pick one your phone can actually carry before downloading anything. Skip the DIY? PrivateLLM deploy sets up your private LLM on AWS for $50 plus usage. Your data never leaves your cloud.