I have found a thread in ionic on this topic: http://forum.ionicframework.com/t/making-phone-call-from-app-href-tel-123/1968/11.
It mentions the whitelist plugin: https:
I try it in a tag it worked on android:
a
First add cordova-plugin-whitelist
cordova add plugin cordova-plugin-whitelist
Then add following lines in config.xml
Finally in a tag use line below