Amazing results from Rootschat! Thank you all very much indeed. MaxD, thanks for the explanation - I'll follow up the link you give in case the con sheet does have a bit more info about Phyllis. I'm sure your reply will help others who are also scratching their heads about marginal scribbles on the register.
William and Rosie - I can't tell you how amazed I am at your replies. I thought I'd pursued every line of enquiry. Phyllis is the last sibling to trace, and I hope maybe it will lead to a living relative who could answer some of the questions I have about a family I never knew. And after one posting on this forum I have more information than I've gathered in the last ten years.
Rosie, how do I find the electoral register for 1937? I don't know whether it would contain any extra information (maybe a partner at the same address) so it could be vital.
William, that is indeed Phyllis's date of birth. Mombasa could well explain her absence from any records here. Again, could you tell me where you found this information? I subscribe to ancestry and findmypast and would be very interested to see if the records give any hint as to a partner who may have travelled with her. Also, as I know she was in the UK in the 1980s (not sure whether this was a short break or whether she had at some point returned permanently) maybe she will be shown in the return listings. As I didn't know the family, and they've all passed away now, I had no inkling that she had left the country.
I can't thank you all enough - I have a pile of death certificates and wills from 'wrong' Phyllises that I've bought over the years, and these are the first positive mentions I've had - very grateful I took out the sub for the 1939 register as it motivated me into making this posting.
Lesley