According to Russian security firm Elcomsoft, Apple saves up to four months of your iPhone call history to iCloud.
Things like phone numbers, times of call and the date are stored in iCloud and this is not something that Apple advertises.
Ever since the release of iOS 8, Apple declines government requests to extract information. According to Apple, “On devices running iOS 8 and later versions, your personal data is placed under the protection of your passcode. For all devices running iOS 8 and later versions, Apple will not perform iOS data extractions in response to government search warrants because the files to be extracted are protected by an encryption key that is tied to the user’s passcode, which Apple does not possess.”
So far, we had no reasons to doubt this policy. However, we’ve seen Apple moving more and more data into the cloud. iCloud data (backups, call logs, contacts and so on) is very loosely protected, allowing Apple itself or any third party with access to proper credentials extracting this information. Information stored in Apple iCloud is of course available to law enforcement.
You can actually turn this feature off on your iPhone, what you need to do is turn off the iCloud Drive function and this will disable it.
Source Elcomsoft, Macworld