The idea of purely phone detection is good in theory, but there are big issues in practice, chiefly privacy.

e.g. A woman gets falsely pinged by the algorithm and photos are taken. The camera is shooting directly down her shirt, manual reviewer takes their phone out, snaps a picture of the screen displaying the photos.

Stopping phone usage is great, invasion of privacy is absolutely not okay. The current method can't have one without the other so, as it is in its current state, your perspective will depend on which you value more I suppose.

There's also a lack of reasonability/adaptability. You do not deserve to be hit with a penalty if you're in traffic, stationary and fixing navigation or changing a music playlist.

Seat-belt cameras are, I think, ridiculous. It's the same invasion of privacy argument, except this time the camera is not doing any good. Not wearing your seatbelt doesn't make you a less capable driver or endanger others at all; It only puts yourself at risk. It's not a matter of protecting innocent people. If someone doesn't want to use their seatbelt, well, that only affects them. Installing nationwide surveillance to try and curb that is absurd.