using System;

using System.Text.RegularExpressions;   

public class Program

{

    public static void Main()

    {

        var rgx = new Regex(@"^\+\d{1,3}\d{10}$",RegexOptions.Compiled | RegexOptions.IgnoreCase);

        var validMobileNumber = "+9198467593293";

        Console.WriteLine("Is valid phone number " + rgx.IsMatch(validMobileNumber) );

        var InvalidMobileNumber = "+91984675932934";

        Console.WriteLine("Is In valid phone number " + rgx.IsMatch(InvalidMobileNumber) );

    }

}