How do you move things out of the iPhone storage to the iCloud storage?
How do I free up space on the iPhone storage, by moving it to iCloud storage?
iPhone 6s, iOS 13
See the following from About storage on your device and in iCloud - Apple Support
Free up space on your device
You can make storage space available on your iPhone, iPad, or iPod touch when you use iCloud Photos and turn on Optimize Storage. Or you can remove content from your apps—like photos, music, and Podcasts—or delete the apps that you're not using.