How to validate phone number using PHP? [duplicate]

Here's how I find valid 10-digit US phone numbers. At this point I'm assuming the user wants my content so the numbers themselves are trusted. I'm using in an app that ultimately sends an SMS message so I just want the raw numbers no matter what. Formatting can always be added later

//eliminate every char except 0-9
$justNums = preg_replace("/[^0-9]/", '', $string);

//eliminate leading 1 if its there
if (strlen($justNums) == 11) $justNums = preg_replace("/^1/", '',$justNums);

//if we have 10 digits left, it's probably valid.
if (strlen($justNums) == 10) $isPhoneNum = true;

Edit: I ended up having to port this to Java, if anyone's interested. It runs on every keystroke so I tried to keep it fairly light:

boolean isPhoneNum = false;
if (str.length() >= 10 && str.length() <= 14 ) { 
  //14: (###) ###-####
  //eliminate every char except 0-9
  str = str.replaceAll("[^0-9]", "");

  //remove leading 1 if it's there
  if (str.length() == 11) str = str.replaceAll("^1", "");

  isPhoneNum = str.length() == 10;
}
Log.d("ISPHONENUM", String.valueOf(isPhoneNum));

Since phone numbers must conform to a pattern, you can use regular expressions to match the entered phone number against the pattern you define in regexp.

php has both ereg and preg_match() functions. I'd suggest using preg_match() as there's more documentation for this style of regex.

An example

$phone = '000-0000-0000';

if(preg_match("/^[0-9]{3}-[0-9]{4}-[0-9]{4}$/", $phone)) {
  // $phone is valid
}