I recently completed a complete upload of my photo library from my mac's photos app (whose local repository constitutes the complete set of my pictures) to iCloud photo library. Wary of future issues if I had activated iCloud photo library on my phone simultaneously. I let this upload complete before activating iCloud photo library on my iPhone. This turned out to be a well founded precaution, because after turning iCloud photo library on my phone today, about half my photos are no longer accessible on my phone, but they are still on my mac and iCloud.com.
On my collections view in my iPhone's Photos app, I started by having many hundreds to a few thousand photos per year from 2008 to 2018 for all years. After turning on iCloud photo library, I now have no photos from 2008 or 2009, and only a handful remaining from 2010 to 2016. The photos that remain in my photos app might be only the ones that I took on my current phone (which I bought in 2016). How do I get the entire set of photos that are currently stored in iCloud photo library onto my phone again?
Edit: A more specific and descriptive timeline of events below:
Let set "A" be all the photos that I want to exist on my mac, my iPhone, and iCloud. 1 week ago, my iPhone had A stored locally and iCloud was off. I then imported A from my iPhone to Photos on my mac. Now A is on my mac and my iPhone locally (iCloud library is still off). I then turned on iCloud library on on my mac and the upload occurred for about a week. As of this morning, A was in iCloud completely.
After I confirmed that, I turned on iCould library on my iPhone, a device that had A stored locally already! Despite this, about 8 years worth of photos (2008-2016) are not accessible on my phone anymore! There should be no deletion / downloading between iCloud and my Phone because the set of pictures in both places was the same!