I have just added this interesting Fel Temp Phoenix to my collection. The mint mark is SMKϚ - the last character looks like an S but I think it is a digamma, so sixth officinae. Cyzicus is a scarce mint for the Phoenix type; I have not been able to find another image of this sixth issue. The Cyzicus coins I have viewed seem to share the same common feature of a quite detailed Phoenix.
AE Half Centenionalis
Constantius II, 337-361 CE
Diameter: 17 mm, Weight: 2.84 grams, Die Axis: 6h
Obverse: D N CONSTANTIVS PF AVG
Diademed and draped bust to right.
Reverse: FEL TEMP REPARATIO
Phoenix standing right on globe, star in field to right.
Mint: SMKϚ (digamma, sixth officinae) star in field: Cyzicus
Two other Cyzicus Phoenix issues (not mine), the first (epsilon) sold by Tom Vossen and his image, the second (gamma) an example from Wildwinds and Biggy Clegg's image.
here's another example
http://www.nummus-bible-database.com/monnaie-35057.htm
Thank you Victor! Although it's not immediately obvious from my poor photo, this looks to be a reverse die match to my example.