>cheap smartphones
disagree. you get surprisingly powerful smartphones within 100-150$ range. Since you anyway have to shell out close to 100$ for a decent smartphone, many extend that to 130$ (10,000 Rs - a phycological barrier) to get a quite good smartphone - thanks to plenty of Chinese mobile manufacturers.
The argument was not that cheap smartphones cannot handle email apps (or such); but these phones can only have so many things and definitely no expectation to have hardware based security features.
You probably don't need hardware security features. OS-based software U2F would probably be a step up (prevents sim-jacking, but physical access to the phone is possibly more vulnerable)