A phone script is a pre determined script that can be read while in a dial session. You can create a phone script by going to Contacts in the top middle, then clicking the Gear icon to the right and selecting Emails and Phone Scripts from the drop down. (Please note this is not available in the Salesforce Application)
Below is an example of where the phone script will appear while in a dial session. Please note that before the dial session begins, you need to select the phone script you would like to appear.