Apple cloud computing system problems shared phone’s directory

I share an Apple computer with my spouse and we are up to date with programs especially our operating system. Though we use the same machine, we still have different account for media player programs and email account. However, we found that the directory of the other is visible to both our phones.
We think the cloud computing application automatically integrated contacts from our devices, and shared all data to the two separate phones.
Is this really what happens when you use this cloud computing application?
