Understanding iCloud Photo syncing and selective syncing with iPhone

gnosislibrarian wrote:

I am trying to understand photo sync'ing with iCloud and have two sets of questions:

Is this accurate:

If I delete a photo from my phone while using iCloud syncing and my iCloud storage is set to Optimize iPhone storage then iCloud will sync a lower quality/lower resolution version back to my phone.

Is this accurate:

I'd like to save iCloud storage to only the items that I really want, while keeping everything on my phone. According to this, it is 'impossible' to selectively sync specific photos to iCloud.

[Re-Titled by Moderator]

Set up and use iCloud Photos - Apple Support