Offload LRC photos from iPhone

I'm not using LrMobile.  I am using the camera app in LRC.  When I first posted this question and you answered so quickly (thanks!), you also provided a link in response to Charlie.D's reply.  Your link seems to presume that I am using the LR Mobile app, right?  (But thanks!)

By @web1305

There is no "camera app in LRC". LRC refers to the Lightroom Classic app which only runs on computers running either the MacOS or Windows operating systems, i.e. it doesn't run on phones. The "camera app" is actually just a camera tool within the Lightroom for Mobile app (the typical shorthand for which is LrMobile) and which as it's name suggests only runs on mobile devices running either Android, iOS or iPadOS. So, if you are using the camera function within the Lightroom app on your iPhone, you are definitely running LrMobile.

The good news is that you are obviously using an Adobe subscription and in that case any pictures you take using the iPhone are automatically synced to your Adobe cloud account. From there they can download into any other of the Lightroom apps that you might be running, including Lightroom Classic on your MacBookPro....which is what you appear to be doing. In that case, once they are safely stored in your LrC catalog, it would be perfectly safe to delete the images from your iPhone in order to create space for more. However in order to avoid accidentally deleting images from the phone which may not yet have synced to the cloud, the usual recommendation is to do the deletion from within LrC on your MBP (i.e. in that way only images that have fully synced are deleted). To do that in LrC simply select the All Synced Photographs special collection which you'll find below All Photographs in the Catalog Panel, right click on the images you want to delete from the cloud, and select "Remove from All Synced Photographs" from the right-click menu. 

 As its name suggests, All Synced Photographs is a list of all the photos that are currently synced to your cloud account, and thus if you remove any images from the All Synced Photographs collection (do NOT remove them from the LrC catalog!) they will automatically be deleted from the cloud account and thus from any other synced devices, including your iPhone. Removing images from All Snced Photographs, however, does not delete them  from LrC, they are merely removed from that collection, and they will still be accessible in LrC via their containing folders.

An alternative approach would be to use the Clear Cache command in LrMobile as @Charlie.D suggested. That should physically delete those original images from the iPhone, but retaining them in the Cloud (they would be replaced with a preview on the phone, so you would still have access to them on that device). However, if you then start editing them on the iPhone the full-size original would automatically be downloaded to the phone.

A third approach would be to proceed with the deletion via All Synced Photographs as per the details above, then once deleted you could ADD them back to the All Synced Photographs collection, which would cause LrC to upload smart previews of the images back to the cloud, so they would be available again on the iPhone but only in that smart preview format. Smart Previews are smaller dng "proxies" which are only 2560 pixels on the long edge (good enough in most cases on the phone) and typically only take up between 1 and 2 megabytes.