Phosgene is COCl2. Halon 1301 is CF3Br (there are a bunch of different kinds of Halon--see wikipedia below). There is no chlorine in Halon 1301, thus it cannot turn into phosgene. Period.
https://en.wikipedia.org/wiki/Halon
Yes, CF3Br (Halon 1301) is bad for the ozone. It's why production was banned. It remains a valuable fire extinguisher material for some critical applications, thus can (and should) be reclaimed professionally. It is relatively safe (obviously it poses an asphyxiation hazard since it removes oxygen from a fire). It also has value. A reputable fire extinguisher company will give you good advice on the best way to sell it (assuming the extinguisher still has gas in it).