If you've imported the photos into Lightroom *and they have synced to the cloud* then it is safe to delete from the camera roll. I prefer to import straight to Lightroom from the camera card, because importing to Camera Roll first triggers the iCloud photo sync, and then importing to LR triggers the Lightroom cloud sync, so you have the same photos syncing twice to two different services. This is even worse if you're traveling and in a hotel, since uploading 70Gb of photos even once is a challenge, much less twice.
As a result, I tend to import to Lr from my card, but keep the card (don't erase it) until I get home and ensure everything is properly synced. I also carry an external drive which I also copy the photos to at the same time as I import, so I have multiple copies.
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