people can not hear me on my iPhone

Did you recently get the iPhone and does it still have the factory screen protector on? if so, you will have to remove it.

Ccall volume level is separate from music and system sounds level and is separate for headphones and speakers. To make call level higher you must do it while you're on the call.

Are you female?

I've heard tale of a rash of issues with makeup / debris in the receiver mesh by the earpiece.

Take a bright light and look at the receiver to see if its clear.

If not use a painters brush to attempt to clear it.