Even if you have linux, there are still third parties that have control over your hardware. Even if you're using graphenos, you can't block the sim or the cellular radio stack, and likely other modules on the SoC, from at-will access to every sensor on the device. You can at least protect your files, unless there's a mitm or other vector that graphenos can't cope with. And at worst, they can simply clone all your encrypted bits and wait on Moore's law or sufficient cubits to go back and crack the copy, on the off chance there's anything they want with your data in the first place.