Your phone shows a number you don't know, or even one that looks local or official, and you're not sure whether to pick up or call back. You usually can't tell from the number alone, because scammers can fake what shows on caller ID. Here's how to handle unknown callers and cut down on spam calls.

⚡ The short version

Don't answer numbers you don't know. Let them go to voicemail. A real caller can leave a message.
If you answer and it's a recording or something feels off, hang up. Don't press any buttons, even “press 1 to be removed.”
Don't call back a number from a voicemail or text. To check, call the company or agency using a number from their official website or your statement.

Why you can't trust caller ID

Scammers can make any name or number appear on your screen. This is called spoofing. They may show a local number (“neighbor spoofing”, often close to your own number) or the name of a real company or government agency, such as the Social Security Administration or the IRS. The FCC and FTC both warn about this. So a number that looks familiar doesn't prove the call is real, and a search for the number may not tell you much either.

Signs the call is a scam

It's a recorded sales message you never gave written permission for. The FTC says that kind of robocall is illegal, and probably a scam.
The caller says you won a prize but must pay a fee to get it.
They threaten arrest, fines or a cut-off unless you pay now.
They want payment by gift card, wire transfer, cryptocurrency or a payment app.
They ask you to confirm sensitive information like your Social Security number, a bank PIN or a verification code.
They rush you or won't let you call back.
They say they're from tech support. See Someone called saying they're from Microsoft or Apple.

Step by step: block and filter spam calls

Block one number: open the Phone app, tap Recents, tap the number (or the Info button), scroll down and tap Block Caller.
Screen or silence unknown callers: go to Settings → Apps → Phone → Screen Unknown Callers. Choose Ask Reason for Calling (the caller is asked why they're calling before your phone rings) or Silence (calls from numbers not in your contacts go straight to voicemail).
Add family, doctors and other important numbers to Contacts first, so you don't miss them.

Menu names here are for recent iOS versions. On older versions, look in Settings → Phone for Silence Unknown Callers.

These steps are for the Phone by Google app. Samsung and other phones may use a different Phone app; look for Block or Spam settings in its menu.

Block or report one number: open the Phone app, find the call in your recent calls, tap it, then tap Block or Report spam.
Turn on spam filtering: in the Phone app, tap More options (⋮) → Settings → Caller ID and spam. Make sure See caller ID & spam is on, and turn on Filter spam calls. Filtered calls don't ring, but they still show in your call history. Phones with automatic Call Screen (such as some Pixels) don't show the Filter spam calls switch.

Ask your phone company what call-blocking or call-labeling services it offers. Some are free. The FCC keeps a list of company call blocking resources.
For a traditional landline, a call-blocking device that plugs into your phone is another option.

Your mobile carrier may also offer call-blocking or call-labeling services (some free, some paid). Check its website or ask customer service.

Join the Do Not Call Registry (free)

Register at DoNotCall.gov, or call 1-888-382-1222 (TTY 1-866-290-4236) from the phone you want to register. It works for cell phones too, and it never expires. If you sign up online, click the link in the confirmation email within 72 hours.

Know what it does and doesn't do. The Registry tells law-abiding telemarketers not to call you, so sales calls from real companies should drop (it can take up to 31 days). It doesn't block calls, and scammers ignore it. That's why blocking and filtering matter. And if someone calls offering to put you on the list, that's a scam: it's free and you can do it yourself.

Report a scam or spam call

Didn't lose money: report the call at DoNotCall.gov.
Lost money or gave personal information: report it at ReportFraud.ftc.gov.
Caller ID spoofing: you can also file a complaint with the FCC at consumercomplaints.fcc.gov.

Include the number that got the call, the number on your caller ID (even if you think it's fake), any number they told you to call back, and the date and time.

If you already paid or gave information

Card or bank: call your bank or card company using the number on your card and ask them to reverse the charge.
Gift card, wire transfer, payment app or cryptocurrency: contact that company right away, tell them it was a scam, and ask them to reverse it. Keep the gift card and receipt.
Social Security number: go to IdentityTheft.gov.
A password: change it, and change it anywhere else you used it.

More detail: what to do if you already called, let them in, or paid.

Getting calls from people saying you called them? Your own number is probably being spoofed. The FCC says scammers usually switch numbers within hours. You can add a voicemail message explaining it, and make sure your voicemail has a password.

Is this phone number a scam? Unknown and spam callers