iPad ok. Macbook ok. Iphone 8 doesn't get icloud photos.

Hello.

I set up iCloud Photos on my macbook. Secondly on my iphone and thirdly on my ipad.

All the photos from all devices are in iCloud but only the macbook and ipad are sync to the cloud. The iphone only has whatever it originally had.

Is this a known issue?

I only have 1 iCloud account. My iphone has plenty of storage left.

Thanks.