I haven't found a setting myself.
Whenever the PhpED activates a session it steals focus and I find that very annoying. The only way I can tolerate is with a large or dual monitors, so at least the web browser window is shown to the side of PhpED rather than on top of PhpED.
A workaround is to set the browser window to always be on top. There are various utilities to do that and I use autohotkey. Search for that in this forum and you'll find some information about it plus some sample scripts.
www.autohotkey.com