The diaphragm is a dome shaped muscular partition between the
thorax and the abdomen in mammals.  It
has a functional role in breathing.  Like
all muscles the diaphragm requires a supply of oxygenated blood.  The arteries that supply the diaphragm with oxygen
are the phrenic arteries. 
There are superior and inferior phrenic arteries. The superior
supplies the superior aspect of the diaphragm and the inferior supply the
abdominal aspect of the diaphragm.
I know anatomy is a huge subject and there seems to be a lot
of memorization but here’s a handy tip for remembering the phrenic arteries and
the diaphragm.
They both have “ph” in them creating the “fa” sound.  You don’t see “ph” too often in anatomical
structures.  Phrenic arteries and
diaphragm are two of them.