You can set your new iPhone as the place to share your location by going to the Me tab in Find My and following the instructions on Apple's support page called Share your location in Find My on iPhone
Note specifically the second point on that page which advises: If your iPhone isn’t currently sharing your location, scroll to the bottom, then tap Use This iPhone as My Location.
I'd also check the status of your old iPhone in Settings > [your name] > [iPhone name]
The device name will be in the list of your devices below. If it is in the list touch on the name, wait for it to establish the profile page then at the foot of that page touch on the line in red which says "Remove from account".
When you erased your old iPhone you would have had to first deactivate your Find My sign in?