>I'd argue that a mobile phone is not an adequate platform for coding. The touchscreen and keyboard layouts make it difficult to type needed symbols, distracting from the problem at hand.
Something akin to hypercard could be made to work very well on a smartphone, or possibly a dataflow environment like PureData but more general purpose. But yeah, 99% of people just want to use their phone and development for phones is much simpler on a proper computer.