Sony XA2 microphone in call on loudspeaker

Hello.
My mother uses Sony XA2 and talks on loudspeaker often. After some complaints, I just tested it in conversation. The sound I hear when she talks to me on loudspeaker is less loud than when it is not on loudspeaker. But also it is kind of muted, like she talks behind something or maybe far away, not sure how to explain better. That muted voice is a bit of problem. I do not know if it is the phone or the OS, because we have not used it on Sony OS. My question is if anything can be done to improve the microphone when on loudspeaker?