string mobile = "";
var mobile1 = Regex.Replace(mobile, "(\\d{3})\\d{4}(\\d{4})", "$1****$2");
Console.WriteLine(mobile1);
Console.ReadKey();
string mobile = "";
var mobile1 = Regex.Replace(mobile, "(\\d{3})\\d{4}(\\d{4})", "$1****$2");
Console.WriteLine(mobile1);
Console.ReadKey();