Photos on iPhone XS

Hello SKWeavie,

Welcome to Apple Support Communities. I understand from your post that not all of your photos are on your iPhone but all of them do show on your iMac. I am happy to help.

Let's check the storage on your iPhone to ensure you have plenty of storage to house all of your photos.

How to check the storage on your iPhone, iPad, and iPod touch

If your findings are that there isn't enough room for all of your photos, I would recommend trying to save space on your device and turning on iCloud Photo Library so you can view all of your photos on all of your devices.

"Save space on your device

iCloud Photos keeps all of your photos and videos in their original, high-resolution version. You can save space on your device when you turn on Optimize Storage.

On your iPhone, iPad, or iPod touch:

1. Tap Settings > [your name] > iCloud.
2. Tap Photos.
3. Choose Optimize [device] Storage.

On your Mac:

1. Open the Photos app and click Photos in the menu bar.
2. Click Preferences.
3. Go to the iCloud tab and choose a storage setting.

If you turn on Optimize Storage, iCloud Photos automatically manages the size of your library on your device. Your original photos and videos are stored in iCloud and space-saving versions are kept on your device. Your library is optimized only when you need space, starting with the photos and videos you access least. You can download the original photos and videos over Wi-Fi or cellular when you need them. You can use Optimize Storage on your iPhone, iPad, iPod touch, and Mac.

If you turn on Download Originals, iCloud Photos keeps your original, full-resolution photos and videos in iCloud and on your device."

Set up and use iCloud Photos

Keep me posted on your progress.

Have a great day!