The blue is actually bioluminescent plankton

Something is up with my phone, I think

No. Not you or your phone. It is rather low resolution and loaded with jpeg noise.

But the original isn't like this. It's only when I upload them on here that it happens.

If that's the case, then what might be happening is because it's so large, the uploader might be scaling it down.
Just a guess.

"i can paint with all three colours of the wind." - me, another colour blind