Wanted to bring this back - the mystery voice of "Phillip Jeffries" (who is not Phillip Jeffries) talking to Mr. C in Part 2 of Season 3.
Theories abound as to who the caller really is, but the most popular one of late is that this voice belongs to Grace Zabriskie, a.k.a. Sarah Palmer, the apparent host for Judy. Judy is linked to BOB as his/its 'mother' and/or mate. Mr. C was also searching for Judy and/or access to the White Lodge, though he did not seem to know exactly what Judy was. He funded the 'glass box' experiment in New York which led to what appeared to be Judy appearing in the box and killing the two youngsters in Part 1 - this suggests that this is what it means when the voice references New York.
Here's the original, distorted voice:
Here is a pitch-shifted clip:
After hearing Grace in a podcast interview, I highly suspect this is her voice, given her clipped way of normally speaking and certain intonations.
Meanwhile: