Hello All,
I too had the issue of my speakerphone conversation not working properly and the other person couldn't hear me speaking. After researching and attempting all of the fixes I could find online and resisting the hated factory reset, I dug a little deeper and found that the Note 9 has not one, but two microphones. One microphone at the top of the phone on the right-side and the other on the bottom, next to the speaker, which is also on the right-side of the phone. Here is the image link.
Anyhow, I left the plastic phone protectors/shipping covers on the front and the back of the phone to keep it from getting any oilier or dirtier on either side of the phone until I felt comfortable that the phone wouldn't turn out to be defective in anyway before permanently attaching a Whitestone Dome Glass protector onto the screen. I am a meticulous person and I like to be clean and organized and I planned to leave this film on the front and back of the new phone for a short period of time 
Of course I am going to clean the phone again thoroughly before attempting to put the glass screen protector on the phone as I am sure you all are wondering, but remember, I am somewhat of a clean freak
I figured I would wait a week or two to make sure the phone didn't turn out to be a lemon because my father has been having some issues with his Note 9 and he may have to do a factory reset or send the phone back for a new one. I searched for a diagram of the Note 9 to make sure there was nothing I was missing and sure enough, I found there were two microphones when I thought there was only one microphone. I immediately knew it was me who made the error by placing a tiny piece of tape over the microphone on top of the phone. This happened because I wanted to hold the plastic film on the front of the phone in place to keep the OtterBox case from peeling it up a little once the phone case was in place. Not knowing this would affect the proper operation of the phone whatsoever, it caused the speakerphone not to function at all because the phone has to have both microphones active and uncovered in order for the speakerphone to work properly.
I removed the piece of tape that was covering the top microphone, dialed Target and immediately placed them on speakerphone as a test. The speakerphone worked as it should and the other person could hear me just fine
So, for those of you who may be like me and placed tape on the edges of the removable film to keep it from peeling off of the phone, please make sure you didn't place tape over the top or bottom microphones 
I really hope this helps those who have been super-frustrated and do not want to do a factory reset on your phone or send it back to Samsung for repair or replacement
