Usually clicking on the book cover will take you to the download. You can download them all here though:
https://phoenixpoint.info/downloads/bv1/
https://phoenixpoint.info/downloads/bv2/
https://phoenixpoint.info/downloads/bv3/
https://phoenixpoint.info/downloads/bv4/
https://phoenixpoint.info/downloads/bv5/
https://phoenixpoint.info/downloads/bv6/