iPhone 11 Pro Max 500GB and iCloud plan

I actually have 125GB of data on my new 500GB capacity iPhone 11 Pro Max. My iCloud plan is 200GB which worked well with my previous 250GB capacity iPhone X. However after upgrading to the new iPhone, my phone has stopped automatically backing up to iCloud. How can this be resolved without buying the next higher 2TB iCloud plan which will be a waste?