Will I lose my photos during an iCloud restore in Photos app on iPhone?

Yes, But it doesn’t back up the Photos, it just synchronizes them across the devices. If you delete a photo on one device, it will disappear from all the devices. to back them up, use services like Time Machine, or just copy them onto a USB flash drive.

You'll want to ensure that you actually back up any important data (iCloud is not a backup but a synchronization service). When iCloud syncs, it. should. sync all images from iCloud onto your device and images on your device into iCloud creating one larger library.

I’m positive. iCloud Restoration only goes one way: it takes photos from iCloud and put them on the device. photos already on the device aren’t affected. I don’t have anything happened to them I know because The same thing happens whenever you add a device to your Apple account that you’ve already used for taking photos: iCloud photos will get added to the device and other photos will stay on the device because they are already on the device.

Of course, I still recommend breaking up your photos if you can, as suggested by @muguy.

For more on iCloud Photos has a synchronization service as opposed to a back up service, see Three Good Reasons for Using iCloud Photos and When Not to Use it

Any Photos that aren’t backed up will be safe, as they are safely on the device. You can safely restore photos from iCloud.

Oops I meant backing up not breaking up…dictation problem