Still mystified as to why my phone calendar tasks all disappeared but success!
Via a 5 year old thread on microsoft forum I discovered that I do have a calendar on
http://calendar.live.com. Fotunately all my calendar tasks from the last 2 years are on there.
I never use outlook or log into live.com & when I went to calendar on my laptop it says "welcome, start here" or something that implies I don't have a calendar - I was reluctant to pursue beyond this as I wasn't sure if "opening" a new calendar account might delete the one I couldn't access & didnt even know existed!
It seems that despite the pop-ups indicating that the phone & laptop were synced, there is no laptop function that recognises this & displays something like "you must activate your account to access your calendar" when you go to the windows calendar tile or for that matter Cortana which only shows generic calendar suggestions, no hint of calendar.live.com
So I'm pretty happy but it could have been easier!