Since the official release of Chrome headless, the main maintainer of PhantomJS has stepped down [1]. With Chrome headless (and official headless support also coming in Firefox) PhantomJS is just becoming painful to use compared to the alternatives.
It does not have a modern JS support and it is slower than Chrome.
Tuleap tests should use Chrome/Chromium headless instead of PhantomJS.
[1]
https://groups.google.com/forum/#!topic/phantomjs/9aI5d-LDuNE