Setting the Contact Do not Call field value to true is a solution that can prevent one-click calling to customers who have set their communication preference to email only or text only. The Do not Call field is a standard field on the Contact object that indicates whether the contact does not want to receive phone calls. Setting this field to true will disable the one-click calling feature for that contact and show a warning message if an agent tries to call them. Verified References: : https://help.salesforce.com/s/articleView?id=sf.contact_fields.
htm&type=5 : https://help.salesforce.com/s/articleView?id=sf.dialer_one_click_calling.htm&type=5