At this point, we need to note that while Russell was alive, the Watch Tower Society of his day did not claim any authority, nor did Brother Russell believe in any "central authority" here on earth (other than Jesus and the apostles through the Bible). Russell did not speak as being the head of a religious organization, such as the Jehovah's Witnesses. All Bible Students were free to accept or reject his conclusions. For documentation, see:
Charles Taze Russell, Authority and Organization
Russell and the Occult
However, the word "occult" itself simply refers to something that is secret, but which secrets are known to a few. Everything that is labeled "occult" is not necessarily related to some kind of demonism, spiritualism or pagan rituals, etc. One could even refer to the Bible as "occult" since it contains secrets that only those who have God's spirit can appreciate.
While we do not necessarily agree with all Russell's conclusions we are providing links to some of Russell's works in which he mentioned "phrenology."
Condition of Unbelievers in the Resurrection
Evolution and the Brain Age
Nearer, My God to Thee
Reasonable, Harmonious Are Divine Purposes
Phrenology (Encylopedia Britannica)
Neuroscientists put the dubious theory of ‘phrenology’ through rigorous testing for the first time