I took a plunge & installed Yosemite on my alternate startup drive. Inititally trying to open Phex it asked to install Apple Java. There's apparently a 2015 update to cater for Yosemite https://support.apple.com/kb/DL1572?locale=en_US. Phex still would not open. So I tried opening an alternative Phex version which I suspect I had previously changed the stub file of for Mavericks. Phex opened fine. I don't know if this will fix the issue for you but try the one I uploaded called Phex_for_Yosemite.zip at MediaFire.

I didn't have any problems opening Acqlite (almost same as Cabos) after the Apple Java update.