iCloud is a consumer facing cloud storage service that leverages Apple's cloud Infrastructure. Apple uses a mix of providers to offer iCloud. In addition to their own data centers in the United States, Apple stores data in both AWS and Google Cloud Platform for redundancy and risk mitigation. They are a company that is practicing a multi-cloud architecture when it comes to the storage of objects in iCloud.
in other words
Where your iPhone is when you're not paying attention to it.