Phone number regex validator, C#

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//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            var regex = @"^(?<countryCode>[\+][1-9]{1}[0-9]{0,2}\s)?(?<areaCode>0?[1-9]\d{0,4})(?<number>\s[1-9][\d]{5,12})(?<extension>\sx\d{0,4})?$";
            
            var phones = new [] {
                "02 5555555 x4545",
                "054 5575487",
                "02 5555555",
                "054 5575487",
                "+1 212 7777777",
                "212 7777777",
                "+44 7777 777-777",
                "+44 20 44444444",
                "07777 777777",
                "020 44444444"
            };
            
            foreach(var phone in phones)            
                Console.WriteLine(Regex.IsMatch(phone, regex));
        }
    }
}

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Compilation time: 0.09 sec, absolute running time: 0.17 sec, cpu time: 0.12 sec, average memory usage: 18 Mb, average nr of threads: 5