As above, if the pic is on a social networking site it is very likely reduced down from the original. So it will be worth trying to chase the original. Phone cameras are never very wonderful, but modern ones are better than the older ones, and it isn’t impossible that the original resolution is significantly better than the version you have. (Phone cameras come in anything from 680x480 - which is pretty dreaful, all the way up to 5 mega pixels - which is vastly exceeds the resolution of the cruddy optics the camera usually has.)
You will need to get the owner of the phone to download the photo to a computer and email it to you, and ensure that they don’t resize it from the original. MMS will also cause it to be resized.
Even if the resolution isn’t much changed, each times an image gets munged in format conversion or resizing, it significantly degrades the quality. Always try for the original.