New favorite Greek letter

It used to be pi, because it was cool and you could memorize it and all, but pi ain't got nothin' on phi.

No, not because it is the golden ratio (1.61803399...) or anything.  For something far more exciting than that (at least to me.)

Consider the following:
See that thingy over to the side there?  That's phi.  It's nice and Greek-looking, correct?  Well, it's better than what your first glance may let on...

In physics, we used phi to represent angle measure (for when we have multiple angles and theta is already taken).  So, please note the fantastic things that can be done with phi:

Phi, plus the crappy triangle (I'm not very good with straight lines).

What does this equal?  No, not phi-delta.  It equals....drumroll...

I hope my teacher doesn't mind that I replaced all the phis on my quiz with Deathly Hallow symbols...