Please upload the attached index.html file to a folder on your domain. The folder should be named CallTracking and with your domain name YourDomain.com the URL will be YourDomain.com/CallTracking.
Some Further Clarifications:
The html page may be placed anywhere. In fact it can even be renamed. Your visitors just have to reach it.
So, for example, if the index.html file is uploaded as it is (without renaming) in a new directory (at YourDomain.com) called CallTracking, the URL for your clients would obviously be YourDomain.com/CallTracking
On the other hand, if the index.html file is uploaded as it is to a sub domain, say, CallTracking.YourDomain.com in the public_html or main directory, the URL for your clients would be just that : CallTracking.YourDomain.com
Finally, one could rename the file to something like Login.html (but not change the contents) and place it at the sub domain. In this case the URL would be: CallTracking.YourDomain.com/Login.html