I’ve a lot of space of more than 4.5 gb in the cloud. I recieve the message that my Iphone hasn’t been backed up due of lack in storage space. Please help me with this issue

Please check you have enough iCloud Storage.

Connect to the Internet over WiFI and keep it connected to power.

Please check iCloud available storage vis-a-vis the backup space required.

Alternative: Choose what to backup and what not to.

Settings > [Tap your Name] > iCloud > iCloud Storage > Backups > [Select your Device, if you have more than one] >

Here You have the next backup size

Choose data to backup. Disable the apps which may consume more space and are not important to you. Note this only backup data within App, not the app itself.

Do not forget to tap "Show all Apps" to see all the apps' data that is getting backed up.

Watch the GIF below to know the size of the next backup.