In case it helps anyone, here are the steps I needed to take to get geben working in spacemacs in order to debug local web apps (this in Ubuntu 16.04):

• Add geben package to .spacemacs and reload

 dotspacemacs-additional-packages '(some-other-package geben)

• Assuming you have xdebug installed, add the following to your php.ini file in /etc/php/7.1/apache2/php.ini

[xdebug]

xdebug.remote_enable=On

xdebug.remote_host=localhost

xdebug.idekey=geben

xdebug.remote_autostart=On

• Open the file you’re interested in debugging
• Start geben in spacemacs with M-x geben
• Navigate to localhost/some-app.php in a browser

That should trigger geben. Debugging time!

A bonus note: I didn’t have any luck with geben-find-file when trying to add breakpoints to other files in the project, but using geben-open-file worked (just a little bit more cumbersome.)