Phex should work fine with Java at least up to version 1.8
(Version 1.5 is simply the minimum version of Java for this version of Phex.)
You need to register and be logged-in at the Oracle java site to be able to download old versions (or access the downloads pages):
https://www.oracle.com/java/technolo...downloads.html (version 1.5 also referred to as V. 5) Scroll down to the jre- versions about half way down the page.

Or https://www.oracle.com/java/technolo...downloads.html for the general list of java versions where you can also find jre-1.8.