I think you are referring to CPP bidding also known as bid-per-call. I would recommend checking the following link for more information -
To get started in the most simple form you can go the Ad Extensions tab, click the View: drop down button and select Call Extensions. Click on +New extension and you will be presented with a field to enter your phone number along with different options, the link included above should help you select the appropriate options.
Let us know if you have other questions!
ScottyD, AdWords Top Contributor
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