added mongodb mvc sample

sample/MongoIdentitySample.Mvc/Models/ManageViewModels/AddPhoneNumberViewModel.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MongoIdentitySample.Mvc.Models.ManageViewModels
+{
+    public class AddPhoneNumberViewModel
+    {
+        [Required]
+        [Phone]
+        [Display(Name = "Phone number")]
+        public string PhoneNumber { get; set; }
+    }
+}