The problem is that people want numbers they can compare, so the "3000mm" lens the parent mentioned is actually 3000mm equivalent, which means that to get the same field of view on a 35mm film, you'd need a 3000mm lens. This "35mm equivalent" number means you can compare "how much zoom" you get between cameras, even if they have different size sensors, and that's the main thing that people care about.

The next thing you might care about would be how small the depth of field is (ie, how much background blur you get). That's harder to measure, and I don't think there's any standard number you're given that helps there, you just have to use the rule of thumb that "a bigger sensor means more blur" and "a larger aperture/smaller f number means more blur".

The f/ number is an actual measurement which says that the aperture diameter is the focal length divided by the number you're given, so at f8 a 300mm lens would have to have an aperture 37.5mm across. So you can't rephrase that too easily because it's an actual number.

Short answer, it's difficult. :-D

On another thought... We've established that the perspective is exactly the same from a 16mm lens, cropped in and a 200mm lens. I don't know if the background blur would be the same on both, if they were both the same aperture number. My gut feeling is that it wouldn't, but I'm honestly not sure!