[Problem Solved]
Dear all!
If you are having the same problem as disscussed above, please find a professional iPhone repair store and ask them to check the audio IC, it’s a tiny little chip on the mother board.
I got my iPhone 7 Plus audio IC replaced today for ¥400 (around US$60), and the problem is solved! All phone functions back to normal, phone calls normal, voice memo working, etc.
Tips: If your phone is still under warranty, please search help from Apple Store. If not, get the audio IC checked, and most likely it will work for you as well.
Again, this is not a software problem, it’s the hardware issue, another new update won’t fix it!