No I'm pretty sure if one has a "paralyzing phobia," then one is mentally ill...
Exactly. Mental illness does not mean that you are a raving lunatic who believes himself to be Napoleon that needs to be institutionalized. A phobia that hinders your life, like in this case where you are 300 pounds but refuse to cook for yourself even though it may help you, is not normal (and this is certainly not your only absurd behaviour, as we all know). People who have irrational phobias usually go to see a mental health professional, helping you with these sort of things is their job after all.
Fear of flying, fear of social interactions, etc are things that people don't want to have and they seek help to get better. The fact that you refuse to even consider seeing someone means that you have no interest in improving or getting better and you have accepted an early death from obesity related problems or somesuch.
Of course this is no big reveal, I'm pretty sure everyone reading these "seasons" has figured that much already.