Have you tried already call-only ads? Call-only ads are for advertisers that are looking that users call their businesses. These ads only appear on devices that can make phone calls and when the users click on the ad, the device will do a phone call.
See here an example of a call-only ad
Since September 21, Adwords announced that now advertisers can supercharge the call-only ads with ad extensions. See the example here:
The new Ad Extensions for Call-only Ads
Location extensions – highlight information about your nearby business locations for customers who want to visit your store in person.
Callout extensions – promote unique offers and benefits, such as 24-hour call center service.
Structured snippets – provide more specific details about your products and services using predefined headers like “Destinations” and “ Types”. For example, a rental car company might list various car classes like sedans, hybrids and SUVs.
These new Ad Extensions will increase the ad space on Mobile devices, which normally increase the CTR and the actions on the ads.