Did you also include the whitelist plugin? It is also needed.
I believe so ...
<plugin name="cordova-plugin-whitelist" source="npm" spec="~1.2.1" />
1. The latest whitelist plugin is 1.3.0
2. Its docs contain the proper access intent rule. Read and apply.
Okay, I've changed the version to 1.3.0. According to the documentation:
<!-- Allow tel: links to open the dialer -->
<allow-intent href="tel:*" />
... which seems pretty unambiguous. This actually appeared in the original config.xml and didn't work, so I found the 'open-external' somewhere and tried that. Anyway, it still doesn't work. This app is in all other respects the result of phonegap create.
What device(s) are you testing on?