As to Phil and mental illness, bi polar or ADHD... I don't know. I do know it takes loving committment to write as he wrote, and the torture is that audiences respond, but the gate keepers keep you away from your audiences. He said in a Canadian concert shortly before his death... hope I remember it acurately "Here is a protest for you... a protest song is a song that you don't hear on the radio, because they say the guy can't sing, or the words are no good, while they play the shit they play on the radio."

For those of us who sing truth to power, ( not comparing my self to Phil, a hero of mine, ) it is a constant knot in your gut, when you struggle to be heard and for example in my case, you get introduced to the record exec, who tells you, "if I haven't heard your name by the age of 48 ( back then) you aren't marketable, face it you are over the hill."
The words over the hill are like a knife in your soul. Today, and it was begining in Phil's day, the industry is looking to children to lead the way, and most are writing as Phil put it, the shit you hear on the radio..."
So, as he said, you keep singing, poor weak flesh in the face of cruel cruel men and their cold machines.
Why... because there is nothing else to do, as long as you can and he did until he could not bear the pain anymore.