Include only Scheduled Phone Calls in an Activity Search

Solution is to use Formula (Text) field with the following setup - See screenshots below:

A. For Activity Search:

1. Navigate to Lists > Search > Saved Searches > New. 
2. Select Activity.
3. Under Criteria define: Formula (Text) and enter details below:

 

 Note: User can define other criteria as needed.
4. Add required Results fields. 
5. Click Save&Run. 

B. For Transaction/Entity Search:

 Use the same steps and define the Formula (Text):

Note: User can specify Activity Type.