Phase velocity greater than propagation velocity

[morrobay]

With:
wavelength = 4 meters
frequency = 30 cycles/sec
period, T, = .033 sec/cycle
wave propagation velocity = 120 m/s
wave number ,k, = 2pi/wavelength = 1.57 radians/meter
angular frequency, w, = 2pi/T = 188.5 radians/sec
phase velocity = w/k = 120m/s
In the above propagation velocity equals phase velocity
Question: what values here would vary so that phase velocity is greater than propagation velocity ?

 

[atyy]

http://www.mathpages.com/home/kmath210/kmath210.htm

 

[morrobay]

http://www.mathpages.com/home/kmath210/kmath210.htm

I have a copy of the above but that is in reference to EM waves.
Is it only in the case of electromagnetic waves where phase velocity can be greater than propagation velocity ?

If not then I would like to see a numerical answer to my original question