A recipient at your property can have a phone number and an email address listed in their Contact Info, but they must have a Preferred Contact Method. This means they can only receive one type of notification: email, SMS, or Slack (if applicable).
To set a recipient's Preferred Contact Method, go to the "People" list and click on their name. This will pull up their profile.
Click on the "Edit Contact Settings" tab and look for "Contact Preference":
Click the dropdown menu and choose the person's Preferred Contact Method. Hit the "Save" button when you're done:
If OFF is selected, then notifications won't be sent to the recipient. Only select this option if the recipient has specified that they don't want to receive notifications.