I've always held my phone with one hand, and typed with the index of the other. Granny style. I doubt the thumb finger evolved to perform high-precision tasks.

I've always held my phone with one hand, and typed with the index of the other. Granny style. I doubt the thumb finger evolved to perform high-precision tasks. The index finger did. Anyway today's huge smartphone screens would force to contort and stretch the thumb in obviously unnatural ways.