There is already an IR blocking filter in all consumer cameras and if you are blocking almost all visible light you are eliminating almost all risk of damaging the camera. That's also the reason why your idea of seeing through thin plastic with camera might work worse than you'd expect. The strength of IR blocking varies.

That said, leaving the camera stationary pointing at the sun for prolonged period is not safe in any case because there are a lot of sources of heat inside camera and rarely there is any active cooling. The sensor would at the very least get heated by the adjacent IR blocking filter. Yes, I am sure you can take a lot of photos of the sun with short exposures. No, I am not at all recommending keeping the camera pointing at the sun in fixed position.

I also highly doubt the iPhone is somehow safe from damage without any filters attached. It might detect sunlight and close the aperture and maybe even use ND filter internally (I did not hear of it) for live view but it won't prevent damage if you somehow set up long enough exposure, opened aperture and fix the iPhone pointing at the sun. In that sense it's not safer than any other camera equipped with same speed lens.