How to Validate Phone Numbers in JavaScript, Python & PHP

A practical guide to validating phone numbers the right way — when a quick regex is enough, when you need a real library, and how to get valid test data to check your logic against.

Regex: the quick format check

For a fast "does this look like a phone number" check — say, on a form field before submit — a regex is fine. The most useful one is E.164:

// E.164: + then 1-15 digits, first digit non-zero
const e164 = /^\+[1-9]\d{1,14}$/;
e164.test("+14155550132"); // true
e164.test("(415) 555-0132"); // false — not normalized

Strip formatting first so users can type naturally:

const digits = input.replace(/\D/g, "");      // keep digits only
const us = /^(\+?1)?[2-9]\d{2}[2-9]\d{6}$/;   // loose US/NANP check

The catch: regex only checks shape, not whether the number is real for its country (valid area codes, lengths, mobile vs landline). For anything user-facing, use a library.

libphonenumber — proper validation

Google's libphonenumber encodes every country's numbering rules and is ported to most languages. It is the industry standard.

JavaScript

import { parsePhoneNumberFromString } from "libphonenumber-js";

const p = parsePhoneNumberFromString("(415) 555-0132", "US");
p.isValid();        // true / false
p.number;           // "+14155550132" (E.164)
p.country;          // "US"
p.getType();        // "FIXED_LINE", "MOBILE", ...

Python

import phonenumbers

n = phonenumbers.parse("(415) 555-0132", "US")
phonenumbers.is_valid_number(n)   # True / False
phonenumbers.format_number(n, phonenumbers.PhoneNumberFormat.E164)  # "+14155550132"

PHP

use libphonenumber\PhoneNumberUtil;

$util = PhoneNumberUtil::getInstance();
$num  = $util->parse("(415) 555-0132", "US");
$util->isValidNumber($num);  // true / false
$util->format($num, \libphonenumber\PhoneNumberFormat::E164); // "+14155550132"

Common pitfalls

• Hardcoding one country's format. "10 digits" breaks the moment an international user signs up. Always pass a default region and let the library decide.
• Rejecting valid formatting. Normalize to digits/E.164 before validating, so "(415) 555-0132" and "+1 415 555 0132" both pass.
• Storing the formatted string. Persist E.164; format for display only.
• Confusing valid with reachable. A number can be valid in format yet not actually receive SMS. Only a live send test confirms delivery — see testing SMS verification.

Test data for your validator

To unit-test a validator you need numbers that match each country's real format. Our tools generate exactly that: