When the speakerphone is on in the conference room, do you talk differently?
It's pretty common.
We breathe from a different spot, hold our chest differently, constrict our throats and generally try to shout our words across the ocean.
The people listening on the speaker are used to it. The people in the room with you, less so.
Human beings don't have a long cultural history with microphones. We don't instinctively understand that they actually work. So we shout instead. And shouting changes how we're believed, trusted and ultimately heard.
Learning to use a microphone is a great skill. When you speak normally, it turns out that the microphone has plenty of volts, watts and amps on hand to move your voice all the way to Latvia if you want it to. And then your words will actually be heard.