In Phylogenesis, Foster begins to further expand the history of the founding of the Humanx Commonwealth, which began in his 1982 novel Nor Crystal Tears.

Desvendapur's aspirations lead him to a secret Thranx colony in the Amazon Basin on Earth where he meets a petty human thief turned murderer, Cheelo Montoya.

The Thranx colony in the Amazon Basin is revealed to the Earth community and the diplomatic beginnings of the Humanx Commonwealth are greatly accelerated.

Montoya becomes a celebrity despite his unwillingness to be in the spotlight and Desvendapur's poems he composed during his time on Earth become wildly popular amongst the Thranx.

Publishers Weekly gave the novel a positive review, stating "The novel will be a treat for those who have followed Foster's tales of the Humanx Commonwealth, to which this is a kind of prelude and which began way back in 1972 with The Tar-Aiym Krang, and can also serve as a splendid introduction to both the Commonwealth and its creator."