I ran into this problem with Testem not picking up phantomjs from the command line to run the tests.
npm folder where the installs occur for globals was still owned by root.
If I tried to run phantomjs from the command line it would throw up a stack trace about ownership.
The solution Chown
sudo chown -R the location where the global node modules are installed by npm.
sudo chown -R YOURUSER:YOURGROUP /usr/local/lib/node_modules/
sudo chown -R YOURUSER:YOURGROUP /usr/lib/node_modules/