iphone photos won't upload/download from photo library

Hello!

I'm using an iPhone 4s, IOS 8.3. Already some time ago I realised that the photo stream was not working, but I had no time to deal with it. A few days ago I finally decided to turn on the Photo Library for all of my devices. I have 5000+ photos, enough space on the iCloud. In the meantime almost all of the photos are in the iCloud. I manage to view them on the iPad, but have no luck with the iPhone so far.

I have tried the following:

1. I turned the Photo Library off and on again. When turning it off the phone 'warns' me that it will delete 2 ⚠ photos from the phone, no problem with that so I confirmed. When turning it on again the waiting wheel is turning for a few seconds until I drop (it looks like a 'crash') out of the settings. When I then go back to check the Library it is on again. ... but it didn't change anything ... the iCloud photo screen still indicates that I have all my photos on the iPhone to be uploaded, there is a little progression bar appearing from time to time, but even over the days connected to Wi-Fi and sufficiently charged battery it does not change… and in any case in the iPhone photo app I cannot see any of the photos from the Photo Library… If it’s of any use, I have plenty of space on my iPhone and I switched on the ‘optimise iPhone Storage’.
2. I turned the iCloud off and on again, already several times … didn’t change anything
3. I even did a full reset of my iPhone and after restoring everything, the problem is still not solved.

What am I missing? Would be great if anybody out there could help me!!! Thank you in advance!