Backup Whatsapp "not enough iphone storage"

I have this problem: i'm trying to do the backup of wpp, and tell me that i don't have enought storage, but i have over 20gb free on ICLOUD and 10GB free on my device.

I tried deleting the backup on icloud of whatsapp, and the backup of the device to save storage and do the backup of wpp then, but that doesn't work so i don't know what to do.

I want to reset the phone but if i do that, the whatsapp chats will be deleted.

Some answers?