How can I preview photos from my SD card without importing?

I know all about how to import photos from an SD card. That is not my question. I have an iPhone 7+ and I want to view the photos on an SD card prior to importing them. Preferably full screen, then have the ability to only select the ones I want to import. I know I can do this but really can anyone see details of photos in thumbnails? I want to import maybe 5% of well over 1200 photos at times without having to import all 1200 to delete all but a few. Is there an app or way to do this?