You can sort your Lead List to easily find those lead without a phone number. You will want to do this through the table view. For a step-by-step tutorial, follow the steps below. 

1.  Navigate to your Lead List, by using the left side navigation bar. 

2. Change your Lead List view to the "table view" by clicking on the button next to the actions button in the upper right corner. 

3. There you will simply click on the header for the "phone" column. This will group and sort the list by phone number. See below

Summary

You can sort your Lead List to easily find those lead without a phone number. You will want to do this through the table view. There you will simply click on the "phone" column header. For a step-by-step tutorial, view the entire article.