How to make pixelated iPhone videos look better?

I have to make an AP Chemistry video in iMovie for a group project, and one of the kids in my group took the video on his iPhone (4 or 4S), but it looks extremely pixelated! It didn't look like that when I saw it on his phone at school.
He texted it to my email. Is that the problem? Is it a problem with the way my computer is displaying it or something?
Is there any way to fix it? I'm not sure what to do.
Some research has revealed that it may require "deblocking," but I don't know what software to use that is compatible with my Mac.

There are two possibilities.

One, the movie was shot at low resolution. If that is the case, the only solution is to re-shoot with either better equipment, or a higher resolution setting if the existing equipment has it.

Two, the movie might have been compressed for text-to-email. If that is the case, your friend will need to copy the movie to a thumb drive or a CD, then you can copy up from that device.

But no, you can't take a pixelated movie and magically increase the resolution. The pixelation is a result of the amount of information available. The lower the resolution, the less space the movie takes, because there's less information. The higher the resolution, the more information, the better it looks, but the more space it requires.

If the information is not there, there's little you can do make it magically appear. It needs to be either re-shot or re-copied via some different mechanism.