We have the option to define custom values in the call logs result field, and we can now add more values for this field under Settings--> Custom fields --> Call logs.
Please select the three dots under more to see the display fields and call logs choices.
Despite the fact that "Outcome" is a system field, we now have the choice to add values to it. Then, select Edit by clicking the three dots under More toward Outcome.
By selecting the + sign in the final value, you can add values: