How do I improve the sound on my smart phone speaker?

You're in the garden, the kids have nicked your portable bluetooth speaker and you want to listen to Stevie Wonder's Hotter than July without it sounding tinny. What to do? Get a small bowl and stick your phone in, speaker end down - you'll be amazed how much better your audio sounds. Like doubly better.
(PS Don't leave in full sun, obvs).