Excuse me Jasper but this thread started with the sentence "A common example is the phrase “This is she.” used to answer a telephone."

I am not discussing the pros and cons of "This is she" and "This is her" just saying that (a) no-one says either in British English (ever) and definitely not "this is she" which would sound so weird that if you'd only ever heard one American say it you would have thought they were being sarcastic
(b) in my experience of speaking to US customers over the past 13 years I have never heard a man say either "This is he" or "This is him".

That is all. I am just saying, for the benefit of foreign learners of English, that this is an American female usage (we Brits answer these questions on the phone in a totally different way, as in my limited but not inconsiderable experience do American males).

So my knowledge of formal grammar is irrelevant. I am talking about my knowledge of usage. OK?

In my experience of phoning US customers "This is she" is an Americanism spoken by women only - i.e. the corresponding "this is he" does not exist. In Britain we'd say "that's me", or "speaking", or even "I'm Peter". If the question was "Is that Peter" I would say "yes" or "yes, that's right". The first time I heard "this is she" I thought the customer was being ironic because she was being asked if she was, say, Janet, by an unidentified caller. But now I realise it is a perfectly normal answer from American women - no idea why they don't just say "Yes"!