Google launched call extensions about four years ago within the Google AdWords advertising platform. Prior, you could list any phone number you want, even without it being your phone number.

That is going to change in June 2015. Google is requiring Google AdWords advertisers using call or location extensions to verify the phone numbers listed in their ads for them to actually show up.

Here is the new policy:

How do you verify your phone number?

In the ad extensions tab select “Call extensions” or “Location extensions” from the drop-down View menu to see your phone number verification status. You can then verify your phone numbers using any one of these three methods:

Ensure the phone number used in your extension is present on the website featured in your ad. This means that if the phone number is associated with multiple ads featuring landing pages for different websites, then the phone number must also appear on at least one page for each unique website. The number must appear in text and will not meet the policy if it appears as an image.
Link your Google Webmaster Tools and AdWords accounts.
Add your unique AdWords conversion tracking code snippet to the landing page featured in your ad.

What if you use 3rd party call tracking? You can still use the later two verification options listed above, Google says.

Forum discussion at Google AdWords Help.