Another thing to delete from your phone
Or put a bit of tape over the camera lens.
Because, like google's voice-activated assistant, it will be bloody hard to completely get rid of it. And if you don't get rid of it I'm damned sure it will surreptitiously peek with your cam all the damned time (if it doesn't now, give it a few iterations). There will be times when you really, really do not want that to happen.
It was only a few hours ago, noticing the cam in a newly-acquired, cast-off laptop peering at me that I reached for the tape. After taping it, I had the thought that it would be great if there were a sliding shutter on laptop cams. Now I see it being a good idea on phones too.
Mechanically, I imagine a snap-action mechanism that causes it to be held either open or closed, as desired. Force is required to move it from either stable state to the other. Much better than relying on friction.
It needn't be integral to the laptop or phone. A glue-on device would also work. Integral is better because it would likely have a better form factor.
I hereby put this idea in the public domain. Anybody can implement it with my blessing.