Why can mobile microphones handle high noise now?
What changed in mobile microphones Probably not much.

I am sure that at the time when you had a phone that could not handle a noisy environment there were also phones that could. It depends on the overall design and quality of the microphone and the electronics connected to it.

It can be as simple as adding a variable gain amplifier that can attenuate the signal when the volume gets very loud. On some phones the manufacturer didn't bother adding such an amplifier or choose one with a smaller gain range. It is also possible that the amplifier was present but the software didn't control it properly.

So it is not so much that things have changed in design. What can change is design choices, some manufacturers simply pay more attention than others.