Importing photos that live in iCloud, not my device

I am considering a move from iCloud Photos to Lightroom CC. I would like to get clarity on something first. My iPhone is set up to optimize storage, meaning not all photos live on my device (rather in the cloud). When I import photos into Lightroom CC from my iPhone, what is Lightroom importing? Is it downloading the originals from iCloud and importing those? Or is it only importing the low-res preview file which lives locally on my phone. Obviously, I want the originals imported into Lightroom, not just the previews. I would hope the app was smart enough to do this, but I don't want to assume. 🙂