we changed our iphone and we lost some of our photos
we changed iphone and we lost some of our important photos, files and documents
If your old phone was set to sync your photos into iCloud and you have just set up your new phone to the same Apple ID, it may simply need more time to sync back to the new phone. If you have a lot of stored photos it usually runs as a background process which can take longer than you expect - in some cases overnight. The photos will be there, you just need to be patient.
If you are still not sure, Go into Settings/Photos and check the options there. (If you see "iCloud Photos" is ON, that is exactly what you need so leave it alone, DO NOT turn it off. You could also login to your iCloud storage using a web browser (any computer can do this) and you will see all your stored data. If the photos are there just be patient.