Is this a phosphorous deficiency or something else?

This is a bit anecdotal, speculative...but maybe some of it is interesting. Yes, colder temps can make some plants change colour. But then, that's often a sign of sub-optimal conditions. Phosphorus and carbs *can* be useful in those conditions (cellular energy/heat). Like, the closest thing to "material sunlight" is basically phosphorus, internal cellular energy (ATP). That's imo one of the reasons why roots and seeds load up on phosphorus (since they won't get good sunlight). Personally, from my few seasons of outdoor growing (even in winter), I kinda use extra carbs/sugars and phosphorus in winter.

It's not a problem. Some phenotypes can still carry different genes or colder temperatures can bring out the purple hues

I'd look at giving that thing a bit of phosphorus, calcium and sugars tbh. I mean, that discoloration does seem a bit extreme.

Hi mate, To be honest and don't see anything wrong. Your plant looks healthy and well into flower. Keep an eye on you ph at this time as it doesn't take much to cause nutrient lock out. This usually shows up as a calmag deficiency first. Other than that, keep up the green work. Good luck and happy growing

Looks amazing! The coloration is because of the strain it is. Most plants tend to get some purple in the leaves when they're flowering. I looked through your pics phosphorus issue would look like a zombie plant you wouldn't have a doubt something is off. Hope you reap a nice harvest!

The dark spots on the leaves are indeed a phosphorus deficiency she needs that in flower the red stems are nothing to do with the phosphorus its just the leaf stems natural reaction to intesnse light completely natural :) Just top her up with some bloom feed and you should be golden :) Best of luck for a hearty Harvest :)