Apple's mobile phone has insufficient backup space, so you can delete unnecessary backup files to free up space. Take Apple 8 as an example, the specific operation method is as follows:

1. First, click the iPhone ID in the settings, as shown in the following figure:

2. Then click iCloud, as shown in the figure below:

3. Click Manage Storage Space, as shown in the figure below:

4. Select the unnecessary data, as shown in the following figure:

5. Finally, click Close and delete, as shown in the following figure: