// The Regex not validate mobile number, which is in internation format.
// The Following code work for me. 
// I have use libphonenumber library to validate Number from below link.
// http://repo1.maven.org/maven2/com/googlecode/libphonenumber/libphonenumber/8.0.1/
//  https://github.com/googlei18n/libphonenumber
// Here, is my source code.

 public boolean isMobileNumberValid(String phoneNumber)
    {
        boolean isValid = false;

        // Use the libphonenumber library to validate Number
        PhoneNumberUtil phoneUtil = PhoneNumberUtil.getInstance();
        Phonenumber.PhoneNumber swissNumberProto =null ;
        try {
            swissNumberProto = phoneUtil.parse(phoneNumber, "CH");
        } catch (NumberParseException e) {
            System.err.println("NumberParseException was thrown: " + e.toString());
        }

        if(phoneUtil.isValidNumber(swissNumberProto))
        {
            isValid = true;
        }

        // The Library failed to validate number if it contains - sign
        // thus use regex to validate Mobile Number.
        String regex = "[0-9*#+() -]*";
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(phoneNumber);

        if (matcher.matches()) {
            isValid = true;
        }
        return isValid;
    }

Considering these facts about phone number format:-

1. Country Code prefix starts with ‘+’ and has 1 to 3 digits
2. Last part of the number, also known as subscriber number is 4 digits in all of the numbers
3. Most of the countries have 10 digits phone number after excluding country code. A general observation is that all countries phone number falls somewhere between 8 to 11 digits after excluding country code.

String allCountryRegex = "^(\\+\\d{1,3}( )?)?((\\(\\d{1,3}\\))|\\d{1,3})[- .]?\\d{3,4}[- .]?\\d{4}$";

Let's break the regex and understand,

• ^ start of expression
• (\\+\\d{1,3}( )?)? is optional match of country code between 1 to 3 digits prefixed with '+' symbol, followed by space or no space.
• ((\\(\\d{1,3}\\))|\\d{1,3} is mandatory group of 1 to 3 digits with or without parenthesis followed by hyphen, space or no space.
• \\d{3,4}[- .]? is mandatory group of 3 or 4 digits followed by hyphen, space or no space
• \\d{4} is mandatory group of last 4 digits
• $ end of expression

This regex pattern matches most of the countries phone number format including these:-

        String Afghanistan      = "+93 30 539-0605";
        String Australia        = "+61 2 1255-3456";
        String China            = "+86 (20) 1255-3456";
        String Germany          = "+49 351 125-3456";
        String India            = "+91 9876543210";
        String Indonesia        = "+62 21 6539-0605";
        String Iran             = "+98 (515) 539-0605";
        String Italy            = "+39 06 5398-0605";
        String NewZealand       = "+64 3 539-0605";
        String Philippines      = "+63 35 539-0605";
        String Singapore        = "+65 6396 0605";
        String Thailand         = "+66 2 123 4567";
        String UK               = "+44 141 222-3344";
        String USA              = "+1 (212) 555-3456";
        String Vietnam          = "+84 35 539-0605";

Source:https://codingnconcepts.com/java/java-regex-for-phone-number/