Syncing Photos to iCloud+ on a low phone storage space. Help?

I am trying to create space on my iPhone and enabled Cloud+ storage to sync photos and videos on iCloud. However, the sync is not happening and keeps on promoting that there is low space on the device and iCloud can not sync the photos.

What is the way forward? As currently, I am unable to even work on Mails and WhatsApp on the phone as nothing is downloading and nor I am able to send any picture..