*Does the sound come out the same way when recording videos or anything that uses the microphone? No, audio is normal when recording videos and when using other apps that use the mike. Sound is also normal when making phone calls, unless the Speaker button is pressed, which starts the garbling. I don't have a bluetooth headset.
*Does the issue happen with all callers or just certain ones? It happens with all callers if the Speaker is on. Only my voice is garbled, incoming audio on the speaker is fine.
*Since the microphone for speakerphone may be in a different place than the mouthpiece, do you have any cases on the phone that may be interfering with it (blocking it, vibrations, etc.)? There are 2 microphones on this phone (one on the bottom near the USB charge port, the other on the opposite side), I'm not sure which one the Speaker uses. Both appear to be unblocked, the case is not interfering.
*Is the speakerphone microphone clean? It is a new phone and the microphones appear to be clean.