How can I block spam calls on my iPhone?

There is really no way to block spam or robocalls on your iPhone. T-Mobile and Comcast have started rolling out a tool that will alert their subscibers if a call wasn't made by a human, and there is always the National Do Not Call Registry. However, these resources won't put an end to your phone being bombarded with spam calls. The new telecom companies' tool, called STIR/SHAKEN, is not only being rolled out slowly, but it is currently (as of 06/11/19) only available on certain types of T-Mobile smartphones. This leaves AT&T and Verizon customers out in the cold, or stuck with the National Do Not Call Registry, which only reduces the amount of spam calls a person will receive.

Update: Verizon does offer a Call Filter to customers. It lets users report and block unwanted numbers.

iPhone owners running iOS 13 can set their device to send unknown callers directly to voicemail, but this means you will need to ignore all unknown numbers, which isn't always plausible. The feature uses Siri intelligence to allow calls from numbers listed in your Contacts, Mail, and Messages.

1. Open the Settings app on your device.
2. Scroll down an tap Phone.
3. Tap the Silence Unknown Callers slider so it is ON/GREEN.