Can I kindly know as to why you feel this way?

Are you suggesting that INFJs are more melancholic and INFPs are more phlegmatic (instead of how it is presented the other way around here in OP's chart?)

I personally felt that this chart was pretty accurate. I identity myself as an INFP and I definitely have a melancholic temperament.

I'm told to be introverted, reserved, aloof and withdrawn sure but at the same time, I'm also very neurotic and anxious often having trouble maintaining my cool while in stress and phlegmatic types if I'm not wrong, have a very calm, relaxed and composed appearance/demeanor.

Ofcourse, everyone will have all the 4 humors/temperaments within them in varying proportions but, for me the melancholic one is the dominant one, I feel.