Looks like even Disney doesn't let the new CMs in on all the little secrets!
You're not crazy. I read about the phone somewhere and went 'hunting' it on my Spring Break trip. It's an old style phone from 1900 placed up on the wall. Be sure to listen to the whole tape from beginning to end (it repeats) as it's kind of funny. I remember having a 'party line' phone when I was a kid. I also remember listening in on my old neighbor lady's conversation about my new dog.
We usually go under the RIGHT train tunnel and past the Exposition Hall. Look ahead where the buildings start on the right side of Main Street. The Chapaue Shop (I'm not totally sure of the spelling, but it's a store which only sells hats and Mickey ears.) entrance is way to the right. Or...if you start down Main Street go into the very first shop (on the right hand side, they sell candy, fudge, etc), walk straight to the back of the store which turns into the hat shop. The phone is on the wall which is facing Exposition Hall (which would be the right).
Ha! Just keep going 'right' and you can't go wrong! Hope you find it. People walk by that phone all day and never think to pick up the earpiece and listen. They may even look at you strangly while you're doing it. One thing I've learned about Disney is to always pick something up and take a look or listen as you may be surprised as to what you find.

Another reason why we love Disney!