A friend has a iPhone 6 iOS 10.x and we cannot find the photos app. She has activated iCloud storage for photos in settings but we cannot find how to see the albums. I am an Androd user and have zero iOS knowledge.
That’s not an app that’s designed to be removed, so it’s either hidden and you can use spotlight to search for which folder it moved to or the database that records where apps are visible is corrupted.
For the former you want to be sure you have a good backup and then restart the device to see if Spotlight can rebuild. If there is no free space, remove some content and restart again.
For the latter, get a good backup and restore the device.