/usr/share/doc/phonon4qt5-backend-gstreamer-dbg/changelog.Debian.gz is in phonon4qt5-backend-gstreamer-dbg 4:4.7.1+git20140403-0ubuntu1.
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It is a symlink to /usr/share/doc/phonon4qt5-backend-gstreamer-dbg/../phonon4qt5-backend-gstreamer/changelog.Debian.gz