Cleanup local synced files on smartphone?

From time to time as needed I sync i.e. audio files to the smartphone.
After a while space on the phone fills up.
Deleting files with a filemanager doesn’t help of course as files get delete on the server as well, which is not what I want.
Is there a way to tell the android up to simply “cleanup” all local files but keeping them on the server?
thanks for any hint