I want to remove the photos from my iPhone but am petrified I will lose them off my other devices!
This can be done. See below.
Is there a simple way of deleting the photos from my iPhone but still be able to access them from my iPhone when I want?
No.
Yes, you can delete all pictures/videos from your iPhone without touching them on other devices. BUT you cannot achieve two conflicting notions: to remove all pictures/videos from the iPhone, still keep them in iCloud but still view them on the iPhone. When the iPhone syncs pics/vids to iCloud and your other devices, it keeps all devices showing all pics/vids. If you remove them from the iPhone by isolating it from syncing with iCloud. That’s it. To see them, you’d have to sync with iCloud again, in which case you’d get all 29K pics/vids back again.
This is how you can delete all pics/vids from the iPhone whilst keeping them on other devices.
But you have to make critical alterations to your settings to achieve this.
On your iPhone, open Settings, Tap on your Apple ID, then Tap on iCloud, then Tap on Photos.
Turn OFF iCloud Photos
Turn ON My Photo Stream if you want any pictures taken on your iPhone to be visible on your iPad or Mac - assuming that My Photo Stream is turned ON in those devices.
Now go back to Settings > Photos
Again, Turn OFF iCloud Photos
Turn ON My Photo Stream if you want to (see above)
What all this achieves is that the pictures/videos on your iPhone are now isolated from iCloud.
You can still manually backup your iPhone’s data to iCloud - Settings > iCloud > iCloud Backup (Turn On or Off depending on your needs. This will backup all your data plus any pics/vids on the iPhone at that time but will NOT sync them with anything).
When you have completed the above changes, let me give you a tip on the easiest way to delete all your pics/vids. Trying to do it manually will bring about a nervous breakdown!
I am assuming, because you don’t say, that you have a Mac computer. Attach your iPhone to the Mac via USB cable. Open "Image Capture" (Applications > Image Capture app). A window will open. On the left under DEVICES, click on your iPhone. It will be shown with the name you gave it.
On the Right will be all your pics/vids. Click on one of them to highlight it. Then use Command + A to select them all. Now
Right Click on one of them. You will be offered a choice;
"Import all x number" or "Delete all x number". Choose Delete.
This will delete them all; but be prepared, this will take 60-90 minutes because you have 29K pics/vids!
When done, all of them will gone, but only from the iPhone.
Any further questions before you begin - just ask.
Ian