In practice, light gathering correlates to F-stop quite well on most normal modern lenses, transmission losses are very low. The main exceptions are deliberately apodized lenses, which have considerably transmission losses wide open.

For the rest - yeah, f# is just one of important specifications.

You were talking about the light being gathered by the lens. That is mostly determined by the f-stop. Technically it is the t-stop, but they should be reasonably close together not to make a huge difference. Quite the contrary, as the phone lens has less elements than some modern camera lens designs, the phone might suffer less from the difference than the camera lens.

The aspects you are now referring to are about the lens quality. Yes, I would expect a real camera lens to be much better than the lens of an iPhone. There is no doubt about that. But in the posting I answered to, you spoke about the comparability of aperture values.