You're assuming there is such a difference and that it is related to the microphone and ADC.
Background noise is not so much eliminated by the microphone or ADC. To suppress background noise, multiple microphones are used and the actual suppression is done by digital signal processing, either in software or in a DSP.
Audio ADCs are now so cheap to make on a chip that it is not worth the effort to make a lower quality version. It does not save any money so no phone manufacturer skimps on the audio ADC.
With microphones it is similar, for speech almost any cheap microphone does the job for use in a phone. For a studio recording microphone its a different story of course but then size and cost are less of an issue.
If you were able to look into the designs of smartphones you would see that they're all very similar. Even though the parts are different, the specifications for the components will be very similar.
Phone manufacturers consider their designs proprietary information and they will not easily share it so that is why it is difficult to find this information.