/usr/include/phonon4qt5/phonon/experimental/ is in libphonon4qt5experimental-dev 4:4.8.3-0ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/phonon4qt5/phonon/experimental/abstractaudiodataoutput.h
/usr/include/phonon4qt5/phonon/experimental/abstractvideodataoutput.h
/usr/include/phonon4qt5/phonon/experimental/audiodataoutput.h
/usr/include/phonon4qt5/phonon/experimental/audiodataoutputinterface.h
/usr/include/phonon4qt5/phonon/experimental/audioformat.h
/usr/include/phonon4qt5/phonon/experimental/avcapture.h
/usr/include/phonon4qt5/phonon/experimental/avcaptureinterface.h
/usr/include/phonon4qt5/phonon/experimental/backendcapabilities.h
/usr/include/phonon4qt5/phonon/experimental/backendinterface.h
/usr/include/phonon4qt5/phonon/experimental/export.h
/usr/include/phonon4qt5/phonon/experimental/globalconfig.h
/usr/include/phonon4qt5/phonon/experimental/mediasource.h
/usr/include/phonon4qt5/phonon/experimental/objectdescription.h
/usr/include/phonon4qt5/phonon/experimental/packet.h
/usr/include/phonon4qt5/phonon/experimental/packetpool.h
/usr/include/phonon4qt5/phonon/experimental/phononnamespace.h
/usr/include/phonon4qt5/phonon/experimental/snapshotinterface.h
/usr/include/phonon4qt5/phonon/experimental/videodataoutput.h
/usr/include/phonon4qt5/phonon/experimental/videodataoutput2.h
/usr/include/phonon4qt5/phonon/experimental/videodataoutputinterface.h
/usr/include/phonon4qt5/phonon/experimental/videoframe.h
/usr/include/phonon4qt5/phonon/experimental/videoframe2.h
/usr/include/phonon4qt5/phonon/experimental/videowidget.h
/usr/include/phonon4qt5/phonon/experimental/visualization.h