Can you filter that list of customers to show only those who have 'No Response' as their outcome code?
SELECT T1.customer_name ,  T1.customer_phone FROM customers AS T1 JOIN mailshot_customers AS T2 ON T1.customer_id   =   T2.customer_id where T2.outcome_code  =  "No Response"
filter list of customers with 'No Response' as their outcome code refers to T2.outcome_code = 'No Response';