using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string pattern = @"\b([\-]?\d[\-]?){11}\b";

​

        Regex rgx = new Regex(pattern);

​

        var sentence = "This is phone number 0341-2239548 and 021-34223311";

​

        var matches = rgx.Matches(sentence);

​

        foreach (Match match in matches)

        {

            string replacedValue = Regex.Replace(match.Value, @"[^0-9]", "");

            sentence = sentence.Replace(match.Value, replacedValue);

        }

​

        Console.WriteLine(sentence);

    }

​

}