> but absolutely do it over the phone. As kids we constantly used to make fun of our Mum who'd repeatedly say "Oh I know, I know" while talking on the phone

> but absolutely do it over the phone. As kids we constantly used to make fun of our Mum who'd repeatedly say "Oh I know, I know" while talking on the phone to a friend - even though both are Australian, they'd both spent time in the UK where that's obviously a common enough way of acknowledging the person on the other end of the line that the Fawlty Towers' character Sybil would regularly caricature the over-use of it. But from what I've observed Japanese people do tend "un" and "a sou" or "sou desu ka" quite a lot even when talking face to face, far more than we would as English speakers, where we might just grunt occasionally to make it clear we're still listening, but probably rely more on facial expressions/eye contact to convey that info.