/usr/lib/x86_64-linux-gnu/libgnuradio-fosphor.so is in gr-fosphor 3.7.0.2.7b6b996-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgnuradio-fosphor.so.3.7.11
/usr/lib/x86_64-linux-gnu/libgnuradio-fosphor.so.3.7.11