I'm not sure which specific novel 'Mrs Phoebe' is from. There could be many characters named Phoebe in different novels. Maybe it's a character created by an indie author or a relatively unknown work.
The relationship between the mentor and the mentee might be based on real - life examples. Older, more experienced writers often take younger ones under their wing.
Well, Phoebe Smith in Bedtime Stories might be a storyteller. Maybe she has her own collection of bedtime stories that are unique in terms of themes, like stories about magical animals or far - away lands. However, without further details, it's difficult to say for certain what her role exactly is.