Before you can use drphil, you will need to install bundler. If you are using the system version of ruby, you need to use sudo to install bundler:
$ sudo gem install bundler
On modern versions of macOS, attempting to use git will prompt its installation, which is a neat feature. Just type git in the terminal and hit enter. You'll get this dialog:
Then you can proceed to do the normal installation steps.
$ git clone https://gist.github.com/61bcc2b821aa5acb24f7fc88921950c7.git drphil
$ cd drphil
$ bundle install
Then run it:
$ ruby drphil.rb
To configure drphil, you will need to modify the drphil.yml. You can edit it by typing open -e drphil.yml in the terminal.