The problem really is that the mics used in phones are selected to be omnidirection and have a limited (relatively) dynamic range that does work best for normal vocal ranges, also you can talk to the phone rather than to a tiny hole on it.
A directional mic would be better at 'ignoring' more ambient noise, probably £20+ for a working bottom entry level one.
Padded cell would work but they'd probably not let you have the tools incase you hurt yourself