but it still shows space being taken up by my photos on my phone. Why is this?
iCloud Photo library is for keeping your photos in sync and updated soon all devices. They will be stored in iCloud and on your iPhone. You can enable "Optimize storage", then only smaller versions will be stored on the iPhone as thumbnails for browsing.
See: iCloud Photo Library FAQ
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:
- On your iPhone, iPad, or iPod touch, tap Settings > iCloud > Photos or Settings > Photos & Camera, then select a storage setting.
- On your Mac, 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.