Low resolution digital photos can be restored but only as far as the pixels allow. Each image is made up from a collection of tiny pixels, all the colours and shades of the image made from small squares. If large areas of the image are blurred due to a dirty lens, or blurred due to movement of camera or subject, there has to be enough pixel information to correct the problem.
For an example I have included a 100 x 100 pixel image, (enlarged for this article) this is 10,000 pixels in all.
This image seems clear enough and you can make out the pixels very clearly.
Add some grease to the lens and now there is not much detail left . (simulated mobile phone image with and dirty lens)
It would be possible to copy and flip the helmet badge but there is no way an image this blurred can be sharpened or brought back into focus.
Mobile phone lenses are tiny, so any dust or grease that gets on the lens, would cover a larger part of that lens than if it were on a conventional camera, as a result it can blur a large part of the captured photo. Although this image is just 10,000 pixels it could easily be an enlarged head and shoulders section from a mobile phone group shot. No doubt that dust will be obscuring the one person in the photo you wanted to be perfect.
The lesson here is if you are taking mobile phone photos of an event that you must have a record of and you dont have a conventional camera, make sure your mobile phone lens is clean, very clean! If your images get blurred as a result of grease or dust like the above photo, there is very little that can be done.