Telephone conversations

For issues specific to caring for someone with dementia.
My mother seems to be far more aware when speaking to me on the telephone, I am thinking this is because she can't see me and I have said who I am and so pretty much normal conversation takes place.
When I am face to face with her she thinks I am someone else, kids the same, is this unusual?
Don't think it's at all unusual Vicky - before I moved in with Mum I could have a telephone conversation with her and she always knew who I was - but since I've moved in most of the time she hasn't a clue who I am - she's always asking "Where's Sue ?" or "Is Sue coming home tonight ?" etc, etc and when I tell her I am Sue, the usual response is - "not you, I mean MY Sue" Image
Yes, I have the same name as my mothers sister and she rather unflatteringly to the sister insisted I was not her daughter who is short, fat with black hair, close description of her sister I know it isn't me coz I'm blonde, ha, ha.
She thinks I am her sister in law who is blonde and very flatteringly an attractive woman albeit about 30 years older than me Image
On the phone though she knows exactly who I am.