There are two methods that you can try for the iPhone manual iCloud backup. The first method is using the manual backup and the second method is by using the automatic method. From the first method, we need to have our device connected with WiFi connection first. Make sure that the internet connection is in a good quality. For those iPhone devices that still using the iOS 7 or erlier, we can tap the setting option then choose iCloud and go to the storage and backup. However, for those who already have iOS 8 or later, we can just go to the iCloud and choose backup. Then, turn the iCloud backup button on. Tap the backup now but we have to make sure that we still connected with internet connection.
Taken from iphone7manuals.com : In the end, we can check that the iPhone manual iCloud backup is finished by tapping the setting option and go to the iCloud to storage and manage storage then choose the device. The backup will be shown on screen about the time and the size of the backup data. Make sure that your storage space in iCloud is enough.