[fuzzieozzie]

I usually have my foot with me.

Foot + phone + ground = destroyed phone

But, with enough resources they could still read the memory in the phone even if it was smashed.

[ben509]

If the ground is solid and the police let you destroy evidence while they're detaining you.

[abraham_lincoln]

Dump it in a bottle of Gatorade or coconut water.

[marnett]

will the electrolytes aid in the destruction?

[logfromblammo]

It's what electronics crave!

Yes, the conductivity of electrolytes in solution will tend to short out conductive pathways in the short term, and contribute to corrosion of exposed metals later on.