Is there a "safe" app for cleaning up storage on I phone?

Have you tried using the capabilities built into Photos?

Merge duplicate photos and videos on iPhone - Apple Support

There are no safe apps, other than the built in features described by IdrisSeabright.

However, if you mean the same photo appears in multiple albums, those are not duplicates. When you add a photo to an album it just creates a “pointer” to the original photo in the photo library, it doesn’t make a copy of the original photo.