I am trying to work out what photos are stored locally on my iphone and what ones are in the cloud, is there an easy way to do this on my phone without logging onto icloud and literally scanning through thousands of photos to spot any that are missing?
iPhone SE, iOS 17
Except for short delays mentioned by markwmsn, the pictures in iPhone Photos and the pictures in iCloud Photos should always be exactly the same. That's want iCloud Photos does-- it synchronizes Photos in the connected devices.
If you have "Optimize Storage" turned on for your iPhone's Photos, then many of the pictures on the iPhone will be smaller and lower quality to save space, but when you need to zoom in or edit, then the full-sized images will be downloaded from iCloud. But, big or small, all the pictures are in both places all the time.
Except for short delays mentioned by markwmsn, the pictures in iPhone Photos and the pictures in iCloud Photos should always be exactly the same. That's want iCloud Photos does-- it synchronizes Photos in the connected devices.
If you have "Optimize Storage" turned on for your iPhone's Photos, then many of the pictures on the iPhone will be smaller and lower quality to save space, but when you need to zoom in or edit, then the full-sized images will be downloaded from iCloud. But, big or small, all the pictures are in both places all the time.
If you have iCloud Photos active on your iPhone, newly taken photos are supposed to be stored locally on your phone and sent to the cloud. There may be a delay in doing the upload for any of a number of reasons. You cannot tell which photos have not been uploaded, but you can get an idea of how many by checking the status line at the bottom of the All Photos view in iOS 17. (It gets murkier in iOS 18.) The status line may alert you if there is a problem with uploading or downloading.
Having iCloud Photos enabled when your iCloud is full is not a good idea. Not only can you find yourself in indeterminate situations like the one you describe, but Photos will stop sending deleted photos to the Recently Deleted album to prevent additional pressure on the already full iCloud. That removes an important protection against inadvertent deletion.
My phone is no longer synching with iCloud as I have ran out of space, and is therefore only storing photos locally, but there seems to be no way of finding out which ones these are on my iPhone.
How to find out what photos are stored locally rather than in the cloud
