First off, your format validator is obviously only appropriate for NANP (country code +1) numbers. Will your application be used by someone with a phone number from outside North America? If so, you don't want to prevent those people from entering a perfectly valid [international] number.

Secondly, your validation is incorrect. NANP numbers take the form NXX NXX XXXX where N is a digit 2-9 and X is a digit 0-9. Additionally, area codes and exchanges may not take the form N11 (end with two ones) to avoid confusion with special services except numbers in a non-geographic area code (800, 888, 877, 866, 855, 900) may have a N11 exchange.

So, your regex will pass the number (123) 123 4566 even though that is not a valid phone number. You can fix that by replacing \d{3} with [2-9]{1}\d{2}.

Finally, I get the feeling you're validating user input in a web browser. Remember that client-side validation is only a convenience you provide to the user; you still need to validate all input (again) on the server.

TL;DR don't use a regular expression to validate complex real-world data like phone numbers or URLs. Use a specialized library.

var x = '301.474.4062';
    
x = x.replace(/\D+/g, '')
     .replace(/(\d{3})(\d{3})(\d{4})/, '(2-$3');

alert(x);

See A comprehensive regex for phone number validation

Quick cheat sheet

• Start the expression: /^
• If you want to require a space, use: [\s] or \s
• If you want to require parenthesis, use: [(] and [)] . Using \( and \) is ugly and can make things confusing.
• If you want anything to be optional, put a ? after it
• If you want a hyphen, just type - or [-] . If you do not put it first or last in a series of other characters, though, you may need to escape it: \-
• If you want to accept different choices in a slot, put brackets around the options: [-.\s] will require a hyphen, period, or space. A question mark after the last bracket will make all of those optional for that slot.
• \d{3} : Requires a 3-digit number: 000-999. Shorthand for [0-9][0-9][0-9].
• [2-9] : Requires a digit 2-9 for that slot.
• (\+|1\s)? : Accept a "plus" or a 1 and a space (pipe character, |, is "or"), and make it optional. The "plus" sign must be escaped.
• If you want specific numbers to match a slot, enter them: [246] will require a 2, 4, or 6. [77|78] will require 77 or 78.
• $/ : End the expression

This regular expression /^(\([0-9]{3}\)\s*|[0-9]{3}\-)[0-9]{3}-[0-9]{4}$/ validates all of the following:

'123-345-3456';
'(078)789-8908';
'(078) 789-8908'; // Note the space

To break down what's happening:

1. The group in the beginning validates two ways, either (XXX) or XXX-, with optionally spaces after the closing parenthesis.
2. The part after the group checks for XXX-XXX

Let's go by parts, you got three conditions:

1. ALL 9 digits being 0 is not allowed
2. The area code (first 3 digits) cannot be the same digit,
3. The 1st and 4th digit cannot be 0 or 1.

Condition 1 is redundant if you consider condition 3; A simple regex not considering condition 2 is:

/^\([2-9]\d\d\) [2-9]\d\d-\d{4}$/

Assuming you want parenthesis and spaces - (555) 555-5555

Explanation:

• \d matches any digit
• [2-9] matches any character from 2 to 9
• space and dash are literals - match spaces and dash
• {4} is a quantifier - will match 4 digits in this case
• ( and ) are escaped literals - will match ( and ) respectively

Now if we want to consider condition number 2 in our expression, we use

• a negative lookahead ?!
• a capturing group () and
• a back reference \1.

Read some regex reference if you want to fully understand those. The full expression is:

^\(([2-9])(?!\1\1)\d\d\) [2-9]\d\d-\d{4}$

Just to help you build some concepts.
The following regex would match the first seven inputs you provided.

/^\+?\d{2}[- ]?\d{3}[- ]?\d{5}$/

\+? would match a + sign. The ? in it makes the + sign optional.
\d{2} matches two digits
[- ]? matches either a - or a (space). ? makes the occurrence of - or (space) optional.
\d{5} then matches 5 digits.
^ and $ are the start and end anchors.