If I already have a iPhone 11 do I need to backup on iCloud? And how?
Do I need to backup to iCloud on iPhone 11in order to trade in to new phone & how?
iPhone 11, iOS 14
It depends upon how you wish to transfer from your old phone to the new one.
Click on this link --> https://support.apple.com/HT201269 to learn how to "Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch". Select one of the three options: Quickstart, iCloud, or iTunes/Finder.
To use Quickstart you will need to have both phones in your possession at the same time.