If you have enabled the “iCloud Photo Library” and “Optimize iPhone Storage” options on your iPhone, some of your iPhone photos are stored on iCloud. That’s why Photos app won’t import all your iPhone photos, as the photos are not actually stored in your iPhone storage.
Why are not all photos importing from iPhone to Mac?
If you have iCloud Photo Library turned on and “Optimize iPhone Storage” option enabled on your iPhone, this is the most likely reason why iPhoto or Photos app won’t import all your iPhone photos.
Why did only some of my photos transfer to my new iPhone?
If your photos are stored in iCloud and you have set up your new iPhone using a new iCloud account, your photos will not be synced from your web iCloud account to your iPhone and so you won’t see any of your old iPhone photos on your new iPhone.
Why are my iPhone photos not showing up in photos?
Check that Wi-Fi is on and you have an internet connection. Tap Settings > [your name] > iCloud > Photos. Make sure Upload to My Photo Stream is turned on. If you don’t see this option, turn on iCloud Photos to keep your photos and videos in iCloud instead.