Installing and enabling Xdebug in Debian 9
Install Xdebug:
sudo apt install php-xdebug;
Add the following to /etc/php/7.0/mods-available/xdebug.ini:
xdebug.profiler_enable_trigger = 1
xdebug.profiler_enable = 0
xdebug.remote_enable = 1
xdebug.profiler_output_dir = "/tmp"
Restart Apache:
sudo service apache2 restart;
Now, all you have to do is create a debugging configuration in PhpStorm (hopefully :-)), and use Xdebug helper for extra convenience.