Article: Tap the grey app with 2 gears on it. You'll usually find it on the Home Screen. It's near the top of the Settings page. It will turn green {"smallUrl":"https:\/\/www.wikihow.com\/images\/1\/15\/Iphoneswitchonicon1.png","bigUrl":"\/images\/thumb\/1\/15\/Iphoneswitchonicon1.png\/46px-Iphoneswitchonicon1.png","smallWidth":460,"smallHeight":300,"bigWidth":"46","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of an iPhone\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"}. This option is near the bottom of the screen. Doing so will select your entire contacts list as the exception to Do Not Disturb. You will no longer receive calls from people who aren't saved in your Contacts app.  This method blocks calls from any numbers that aren't saved in your Contacts app, meaning that you might miss out on a work- or appointment-based call. Do Not Disturb also prevents other app notifications (e.g., text messages, email, social media) from showing up as alerts.

What is a summary?
Open your iPhone's  Settings. Scroll down and tap  Do Not Disturb. Tap the white "Do Not Disturb" switch . Tap Allow Calls From. Tap All Contacts.