Problem with USRP used for digital beacon reciever

Thank you so much again Josh
So Josh could you give me some opinion
if my input signal pass through the USRP is about cos(wt+phi) after it
passed through the mixer by NCO that generate sinwt and coswt and met
with the cic filter inside the usrp

what my professor expect is
the output that go out of the usrp must be the constant value cosphi and
sinphi so if we connect to usrp with the scope sink, what we would see
is the DC graph of the cosphi and sinphi values but what we notice for
real was the scope showed the graph that seems to have cycles.So what do
you think?
but if what i aspect is wrong . SO how can i find the PHI of the input

Thank you very very much for yours advice

sorry for my english too.