Move or copy photos from iPhone or iCloud to Dropbox

I’m using the latest iOS 12 release, and the latest version of the Dropbox iOS app, on my iPhone X.

I have over 7,000 photos on my iPhone; they are also synced to my iCloud. (The volume consists of pretty much every photo I’ve ever had on an iPhone, beginning with an iPhone 4S.)

Having this number of photos on my iPhone has been making my iPhone quite sluggish.

I tried using the Dropbox iOS app’s built-in feature to copy or move the photos to one of my Dropbox folders; but, on each attempt, the Dropbox iOS app hangs, after moving anywhere from few hundred to a couple of thousand photos.

I then opened the iCloud app in Windows 10, intending to copy the photos en masse to Dropbox, then, once the move was confirmed, erase the photos from my iCloud. (I also tried this through accessing my iCloud via Google Chrome.)

I can’t seem to select more than 1 photo at a time, in my iCloud photos area. As you can imagine, selecting over 7,000 photos, one at a time, is not feasible.

Thank u VERY much, peeps, for any help with this! 🙂