@olibclarke is right, the phase randomised FSC is not included in the text file.
You have to re-arrange the equation from @apunjani above and perform the calculation to yield this curve e.g. in a spread sheet.
So for the sake of having this documented for others. Ali’s comment above relates fsc_n to two columns in the text file (fsc_noisesub_true and fsc_t - “tightmask”), so with a smidge of maths
fsc_n = (fsc_t - fsc_noisesub_true) / (1.0 - fsc_noisesub_true)
will yield fsc_n (or the phase randomised FSC).
Best,
Charles