Hi Nimuie,
Welcome to the Apple Support Communities!
I understand that after turning on iCloud Photo Library, you are seeing different amounts of storage used on your devices and the iCloud website. This could be because the setting to optimize storage is enabled on your iOS devices but not your Mac.
The article below explains how to turn on Optimize [device] Storage on your computer and iOS devices and what happens when you choose to use this feature.
iCloud Photo Library FAQ - Apple Support
iCloud Photo Library automatically keeps all your photos and videos in the original, high-resolution version. Follow these steps to choose how you store your photos and videos on your device:
- In iOS, tap Settings > iCloud > Photos or Settings > Photos & Camera, then select a storage setting.
- In OS X, click Photos > Preferences > iCloud, then select a storage setting.
If you turn on Optimize [device] Storage, iCloud Photo Library will automatically manage the size of your library on your device, so you can make the most of your device's storage and access more photos than ever. All of your original, full-resolution photos and videos are stored in iCloud while device-size versions are kept on your device. You can download the original photos and videos over Wi-Fi or cellular when you need them.
If you turn on Download Originals, iCloud Photo Library will keep your original, full-resolution photos and videos in iCloud and on your device. Download Originals is the default setting for iOS devices with the free 5 GB storage plan and for all Mac devices.
You need an Internet connection to access an original photo or video that’s stored only in iCloud.
I also understand that you would like to know how to delete photos from your iPhone without them being removed from iCloud. If you are using iCloud Photo Library, the photo or video will be deleted from your iCloud Photos Library and iCloud storage.
Get help with your iCloud Photo Library - Apple Support
If you want to remove photos and videos from all your iOS devices, Mac and iCloud.com, you can delete them in the Photos app.
When you delete a photo or video from your Photos app, it will also delete from your iCloud Photo Library and iCloud storage. You can recover your photos and videos from the Recently Deleted album for 30 days.
Best regards,
Joe