Many smartphone camera offer a digital zoom function, but you're almost always best served by pretending it doesn't exist. Even in the liveview preview, you'll be able to see how noticeably your images degrade the second you start to "zoom." The camera is simply extrapolating what's already there and basically guessing what the image looks like. It gets ugly fast.

 

When you're cropping, however, you're actually just sampling pixel info that was actually recorded. Many smartphones have 8-megapixels of resolution and sometimes more. That means you can crop substantially and still have plenty of resolution left for display on the web. And the lack of gross upscaling artifacts will help mask the fact that it was taken with a phone.