When Mac is signed in with Apple ID and password in system preferences , if iCloud Drive and desktops and documents box are checked https://support.apple.com/en-in/guide/mac-help/mchle5a61431/10.14/mac/10.14
These personal documents will be visible in finder > under iCloud section > iCloud Drive > Documents , they will mirror in iCloud.com also , once you delete these personal documents from Mac if other devices like iPhone are also synced in which the same Apple ID and password of Mac is signed on the same network , where iCloud Drive is turned on , they will also be deleted from iPhone and from where it was created that is your Mac laptop as well from iCloud.com
See the article https://support.apple.com/en-us/HT204025
Read https://support.apple.com/en-in/guide/mac-help/mchle5a61431/10.14/mac/10.14
You wrote - I want to keep what I create on the device I created it.
You can disconnect Mac from iPhone , just sign out the Apple ID from Mac https://support.apple.com/en-in/HT208242
And sign in with new Apple ID and password in Mac https://support.apple.com/en-us/HT204053 , the iPhone will not have any impact , those documents that used to sync from the primary iCloud will stay on the iPhone .
The other way is you can move documents from Mac to other location see the last para of the article https://support.apple.com/en-gb/guide/mac-help/mchl1a02d711/10.14/mac/10.14