He's a metaphysical phenomenon of your subconscious mind, a phantasmagoria of your mental faculties.
9 seconds sound clip from the Fun and Fancy Free movie soundboard.
You can hear this line at 01:11:06 in the Blu-ray version of the movie.
Quote context
[...]
- Willie was a nice giant, he was. He just got too big for his britches.
- No, don't touch me. I'll be all right.
- What I'm trying to explain is that Willie the giant didn't actually exist. No.
- He's a metaphysical phenomenon of your subconscious mind, a phantasmagoria of your mental faculties.
- In other words, just a figment of your imagination.
- No!
- Yes. So there's nothing to be upset about.
- Hey! Has anybody seen anything of a teensy-weensy little mouse?
[...]