Welcome to Android Central! Phones pretty much always use a separate mic for the speakerphone -- typically the secondary mic at the top of the phone.
Try recording a video with sound, and then play it back and listen using headphones. If you only hear sound in one ear, then your secondary mic is probably damaged.
It's also worth seeing if this happens in Safe Mode as well, in case some 3rd party app is interfering:
https://motorola-global-en-uk.custhe...148153/p/10837
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