@aaronpk My theory: saying “this is x” on the phone, is a way to link the voice speaking to the name/person. “This voice you hear is x”. In person, they see your face talking, so saying “I’m x” is linking your face to your name more than your voice to your name, so expanding the phone phrase in person to “this face is x” is why it sounds weird.
@DaveWoodX This makes sense, which is why I was so thrown off when 8 different people introduced themselves by saying "this is X" in person today.