Hello Was this ever resolved ? I have exactly the same problem - Can see all my photos on laptop photos and within i-cloud but only have a fraction of these showing up on my phone.
I can see all my photos on my laptop 'photos' and when I go into iCloud but only a fraction of these show on the 'photo' app on my phone. The phone app seems to instantly update for photos taken with my camera but not those that come into my photos from any other source.