I am considering getting a Brian James trailer and towing my Phoenix to Sprints. I was wondering what the situation is with insurance. If the trailer & contents (Phoenix) covered by the main car or do you need separate insurance?

The trailer and contents will be covered by your tow cars insurance (providing you have a license that covers towing!) but third party only. That covers anything or anyone you damage, but not your own tow car, trailer or it's contents.

Assuming your insurance is aware you have a tow bar
We have an extra insurance on the Caravan, that includes towing related problems as well as theft etc

done with http://cover4u.co.uk/

Steve