Either got crushed, something came loose or water damage from sweat. Outside of that, coincidence that it just happened to fail during that time; in any case if its under warranty still just take it in and say there's something wrong with the screen; circumstance doesn't really matter, turned it on and that's how it was.
You can't damage your cell phone with static because your phone isn't grounded. I suppose you could do something if you had it plugged in, charged yourself up, and poked straight at the metal contacts of the processor. Although even then there are capacitors to protect against that sort of thing.
All of the sensitive bits of your phone are well-shielded so no static you could generate by accident would do any damage at all.
That said, it sounds like you got sweat in it and ruined the screen that way. Or it just broke because you hit it on accident while biking. Those are the most likely culprits.
Would be easier if you posted a photo with the phone to figure out whats wrong.
And no static electricity should not be a problem (well unless you get hit by lightning, but then you have some other issues besides your phone).
From your description it sounds like a cracked screen. If its something similar to this [link] is cracked. Nothing you can do about it unless you have warranty that can cover it, or replace the lcd panel - which is not really worth it in most cases.
Not really sure what it looks like when involving a phone LCD screen, but static electricity will destroy circuitry. It basically causes shorts that burn out the circuits. You might not see any effect on the screen unless the shorts occurred in that area or the screen will simply stop working in the areas affected. The other possibility of what happened to your phone is that all the constant bumping around might have caused some circuitry behind the screen to come loose and/or physically damaged. Occasionally electronics have unknown defects in their construction or materials as well, since mass production is never 100% perfect. And all that jostling around might have been all it took for the defects to make a noticeable effect.