Blocking withheld numbers
How to block No Caller ID calls
The short answer
A withheld number cannot be blocked individually, because your phone never received a number to add to a block list. What works instead is handling unknown callers as a group: Silence on iPhone, or your carrier’s anonymous call rejection. Both take about a minute, both are free, and both silence legitimate callers along with the rest.
Checked on iOS 26.0–27.x, Android 15–16 · Updated October 18, 2026
- Time
- 1 minute
- Cost
- Free
- Block one number?
- Not possible
- Block the category?
- Yes
Why the block button does not help here
Blocking works by matching a number against a list. A withheld call carries no number, so there is nothing to match and nothing to store.
Opening a No Caller ID entry in Recents gives you no Block this Caller option, because there is no caller to block.
Blocking one spam number you *can* see rarely helps either — these operations rotate through thousands of numbers and fake them routinely.
From the makers of this guide
Want the calls screened, not just silenced?
PhoneShield answers your calls first. Known scam numbers are refused before your phone rings, the people you know ring straight through, and everyone else is asked who they are and why they’re calling, so your doctor and the delivery driver still reach you.
iPhone: silence the whole category
iOS 26 and later
One setting covers withheld, unknown, private and restricted calls together.
Open Settings > Apps > Phone.
- Settings
- Apps
- Phone
Tap Screen Unknown Callers and choose Silence.
Carrier-level rejection, where offered
Some carriers and most landline providers offer Anonymous Call Rejection, which refuses withheld calls before they reach your phone at all. Where it exists, it is usually toggled with a dial code.
On many landlines, dial **\*77 to switch Anonymous Call Rejection on and \*87** to switch it off.
On mobile, check your carrier’s app — the feature is named differently by each and is not offered everywhere.
- Carrier app
- Call settings
Beyond this setting
What else helps
Blocking is backwards. Screening is the fix.
Everything above works by refusing people before you know anything about them, which is why each one costs you real calls. Screening reverses it: the caller is asked who they are and what they want *before* your phone rings, reported scam numbers are refused outright, and your contacts come straight through untouched. Nothing legitimate gets silently binned. PhoneShield does it on your existing number with no app to install, and it works for a parent on an old handset just as well as for you.
Screening, step by step →Report the persistent ones
The FTC passes reported numbers to carriers every business day, which is how carrier-level flags get built in the first place.
How to report →Got a specific number?
Check who’s been reporting it
See how often people reported a number to the FTC, what the calls were about, and what to do, at isthisnumberascam.com.
Questions
What people ask
How do I block No Caller ID on iPhone?
Not individually — there is no number to block. Use Settings > Apps > Phone > Screen Unknown Callers > Silence, which sends every number outside your contacts, withheld ones included, to voicemail without ringing.
Can I block private or restricted numbers on Android?
Android has no universal setting. Most builds offer a "Block unknown or private numbers" option under Phone > Settings > Blocked numbers, and the exact wording varies by manufacturer and version.
Does *77 work on a mobile phone?
Usually not. Anonymous Call Rejection with *77 is a landline feature. On mobile you need your carrier’s own call-control setting, where one is offered.
If I block them, will they stop calling?
No. Blocking changes what your phone does when the call arrives; it does not remove you from any dialling list. The calls continue — you simply stop hearing them.
What happens to a blocked caller?
With silencing they go to voicemail and appear in your Recents afterwards. With carrier-level Anonymous Call Rejection they hear a refusal message and you get no record at all.
Sources
Checked against
Every step is checked against the official instructions. Menus change with updates; tell us if one has moved.