pip install sphinx
In case pip is not installed then you can follow the following methods to install pip.
General - Method 1:
Follow the below link to install pip for the official pip documentation page, pip.
Linux Users - Method 2:
For GNU/Linux, use the this link
For Mac Users - Method 3:
If you installed python on MAC OS X via brew install python, then pip is already installed along with python.
brew install python