You do know that when you switch to speaker phone it’s often switching the microphone setup, right? Like it’s going from earpiece to conference call setup… it’s not like it stays the same and blows out the other end. We have the technology to control noise input and background. This was ~ maybe ~ true of older phones, but it certainly isn’t today.
I talk on the phone like this due to being a walker & talker. So I pull up my work systems on my phone to update notes and email people as I’m talking. If that were the case the dozens of phone calls a day would tell me I’m way too loud.