Latest iphone back up greyed out

To improve understanding of the phenomenon, it would be highly beneficial if you could share a screenshot. Visual representations carry greater impact than written descriptions.

Please remember that this is a public forum, so when attaching a screenshot, please avoid including any personal credentials such as IP addresses, card details, email IDs, Apple IDs, IMEI numbers, serial numbers, phone numbers, order IDs, or any identifiable location information if you are sharing a map.

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

Ensure that your iPhone is connected to a stable Wi-Fi network. iCloud restores require an internet connection, and a weak or unstable connection can cause issues.

Make sure there is a backup available in your iCloud account. Go to "Settings" > [your name] > "iCloud" > "Manage Storage" > "Backups" to confirm that a backup for your device exists.