Can't backup whatsapp to icloud "enough enough iphone storage"

Dear all,

I have more than enough (more that 2,5x the backup size) available on my Icloud. But i can't back up because I dont have enough space on my phone. WHich is very strange since I want to back up on iCloud and free up space on my iPhone device.

I found a similar post about this subject but the links the support pointed out are of no help. Still dont know how to back up to icloud since my phone itself lacks space.

How to fix this problem. I need more space on my phone and have plenty storage left on my iCloud account.

Thanks in advance