Download the zip package, unzip it, and copy the executable to a system directory in which webshot can look for the PhantomJS executable.
install_phantomjs(
  version = "2.1.1",
  baseURL = "https://github.com/wch/webshot/releases/download/v0.3.1/",
  force = FALSE
)The version number of PhantomJS.
The base URL for the location of PhantomJS binaries for
download. If the default download site is unavailable, you may specify an
alternative mirror, such as
"https://bitbucket.org/ariya/phantomjs/downloads/".
Install PhantomJS even if the version installed is the latest or if the requested version is older. This is useful to reinstall or downgrade the version of PhantomJS.
NULL (the executable is written to a system directory).
This function was designed primarily to help Windows users since it
  is cumbersome to modify the PATH variable. Mac OS X users may
  install PhantomJS via Homebrew. If you download the package from the
  PhantomJS website instead, please make sure the executable can be found via
  the PATH variable.
On Windows, the directory specified by the environment variable
  APPDATA is used to store phantomjs.exe. On OS X, the
  directory ~/Library/Application Support is used. On other platforms
  (such as Linux), the directory ~/bin is used. If these directories
  are not writable, the directory PhantomJS under the installation
  directory of the webshot package will be tried. If this directory
  still fails, you will have to install PhantomJS by yourself.
If PhantomJS is not already installed on the computer, this function will
  attempt to install it. However, if the version of PhantomJS installed is
  greater than or equal to the requested version, this function will not
  perform the installation procedure again unless the force parameter
  is set to TRUE. As a result, this function may also be used to
  reinstall or downgrade the version of PhantomJS found.