On the new phone go to Settings/[your name]/iCloud, tap on Photos. Is Optimize iPhone Storage enabled? If it is then your new phone is saving compressed, lower resolution versions of your photos. iCloud still has the full resolution.
On the new phone go to Settings/[your name]/iCloud, tap on Photos. Is Optimize iPhone Storage enabled? If it is then your new phone is saving compressed, lower resolution versions of your photos. iCloud still has the full resolution.