Moving a large amount of photos to external

Hello i'm in the process of setting up immich and im starting to have a long term plane. I have a large amount of photos from the past stored and organized already and i set it up as an external path for immich so it's even nicer to look at.

Where i ran into a problem is with the phones. I do like the backup feature because it is stupid easy and makes sure i don't lose all my photos is something happens to my phone but every couple of months i still want to move all the photos and videos from my phone and add it to the external library which has even more copies spread out.

But if i do that i'm going to have a bunch of duplicates because immich will see the photos in the external, but still keep the old ones it backed up from the phones?

What is the easiest solution to this?