Welcome to Android Central! Which phone? What data manager are you referring to? If you mean the Settings>Data Usage menu, that simply tracks how much data (either wi-fi or cellular) apps have been using. If you delete apps, they get grouped together in that list under Removed Apps (so if you delete more apps, the data they used in the past cycle add to the Removed Apps category). If you stop deleting apps, then I think that category will disappear the next time your data usage cycle resets to zero. I don't think it's taking up any storage space on your phone.