iPhone space

iCloud storage can only help in a limited way with a shortage of storage on an iPhone. See the information in About storage on your device and in iCloud - Apple Support including the excerpt below:

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.

See: Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Renting iCloud storage space does not add storage space to an iPhone.

If you need additional space on the phone, you will need to delete or move existing content.