As drawn, the Ph212 phasor diagrams are just representations of the complex
numbers at a particular point in time.  (They just don't tell you this!)  The
complex numbers arise from solving the second order differential equation:

E(t) = V_C(t) + V_R(t) + V_L(t)
     = Q(t)/C + R I(t) + L dI(t)/dt
     = Q(t)/C + R dQ(t)/dt + L d^2Q(t)/dt^2

Generally, you are given an E(t) of the form

E(t) = E_max sin(omega t + phi)

and you assume the current is of the form I(t) = I_max sin(omega t) (which
gives you the charge Q(t) as an integral of I(t)).  But this makes the
equation an annoying trig identity bitch to solve.  Fortunately, you can
instead treat the EMF and current as though they are the imaginary parts of
complex numbers, and then write:

E*(t) = E_max cos(omega t + phi) + i E_max sin(omega t + phi)
      = E_max (cos(omega t + phi) + i sin(omega t + phi))
      = E_max cis(omega t + phi)
      = E_max e^(i*(omega t + phi))

I*(t) = I_max cos(omega t) + i I_max sin(omega t)
      = I_max cis(omega t)
      = I_max e^(i omega t)

which gives the voltages across the circuit elements as:

V_C*(t) = -i I_max/(omega C) e^(i omega t)
        = I_max/(omega C) e^(i*(omega t - pi/2))
V_R*(t) = R I_max e^(i omega t)
V_L*(t) = i omega L I_max e^(i omega t)
        = omega L I_max e^(i*(omega t + pi/2))

EEs generally drop the (i omega t) term in the exponential, so their phasors
don't evolve over time, but it's assumed to be there and you can put it back
if you want time evolution in your phasors.  (Then they just rotate about the
origin at frequency omega, completing one full rotation in time 2pi/omega.)

Anyway, both kinds of phasors have length equal to the max voltage, angle
equal to the argument of the sine or cosine function, and the x and y
components are the real and imaginary parts of the phase vector at the time
in question.

Also, from KVL (which we used to get the original diffeq), we can write
that:

E*(t) = V_C*(t) + V_R*(t) + V_L*(t)

and cancelling out the e^(i omega t) factors on both sides gives:

E_max e^(i phi) = -i I_max/(omega C) + R I_max + i omega L I_max
                = (R + i (omega L - 1/(omega C))) I_max
                = Z* I_max

And by equating lengths and angles of the complex numbers on either side of
this equation, we get the usual relations:

E_max = Z I_max
tan(phi) = (omega L - 1/(omega C))/R

Anyway, basically, the two kinds of phasors are the same thing, the Ph212
phasors are just confusingly poorly defined.  ;)