How do I know how well I am progressing in my PhD?
In my observation over some decades (in mathematics), I think it is nearly impossible for a PhD student to gauge their own progress. Sure, it is possible to know whether one feels discouraged or encouraged, etc., but these are mostly artifacts of one's own temperament and of the general environment, not indicators of one's progress.

If you have an engaged, perceptive, competent advisor, they will by-far be the best judge of whether you're on-track or off.

Even then, the real goal is not to measure up to some scalar-valued "good/bad", but to _become_what_you_can_.