F-stop is the relevant property for exposure, but not for the total amount of light collected by the sensor, which is what determines the noise level (all else

F-stop is the relevant property for exposure, but not for the total amount of light collected by the sensor, which is what determines the noise level (all else being equal). Exposure is light per unit area. I do think that focusing on sensor size is unhelpful when thinking about noise levels. Big sensors do not magically collect more light simply in virtue of being bigger. They can only do so if you’re able to put a bigger hole in front of them (again, holding constant the angle of view). The use of very wide apertures is inherently more practical with smaller sensors. As for using wide apertures with a DSLR, this is of course possible, but only in cases where a shallow depth of field is acceptable. On a cell phone camera f1.8 will almost always give sufficient depth of field. Realistically speaking most photos on a DSLR will be taken a few stops down from that. It’s undoubtedly the case that DSLRs have an advantage over phones in terms of noise levels, but you have to consider the whole optical system to estimate the magnitude of the difference, not just the size of the sensor.