refactor:

-Определил общий интерфейс для старницы создания и изменения телефона.

PhoneStore/Controllers/OrdersController.cs

@@ -50,7 +50,7 @@ namespace PhoneStore.Controllers
         {
             order.UserId = int.Parse(_userManager.GetUserId(User));
             order.User = null;
-            _orderService.Create(order.MapToOrderViewModel());
+            _orderService.Create(order.MapToOrder());
             return RedirectToAction("Index");
         }
 

PhoneStore/Controllers/PhoneValidatorController.cs

@@ -15,8 +15,15 @@ namespace PhoneStore.Controllers
         }
 
         [AcceptVerbs("GET", "POST")]
-        public bool CheckName(string name)
+        public bool CheckName(string name, int? id)
         {
+            if (id.HasValue)
+            {
+                return !_db.Phones
+                    .AsEnumerable()
+                    .Any(p => p.Name.Equals(name, StringComparison.CurrentCulture) && p.Id != id.Value);
+            }
+            
             return !_db.Phones
                 .AsEnumerable()
                 .Any(p => p.Name.Equals(name, StringComparison.CurrentCulture));

PhoneStore/Controllers/PhonesController.cs

@@ -47,7 +47,7 @@ namespace PhoneStore.Controllers
         [HttpGet]
         public IActionResult Create()
         {
-            PhoneCreateViewModel model = new PhoneCreateViewModel
+            IPhoneEditable model = new PhoneCreateViewModel
             {
                 Brands = _db.Brands.ToList()
             };
@@ -111,7 +111,7 @@ namespace PhoneStore.Controllers
             if (phone is null)
                 return RedirectToAction("Error", "Errors", new {statusCode = 777});
             
-            PhoneCreateViewModel model = new PhoneCreateViewModel
+            IPhoneEditable model = new PhoneEditViewModel
             {
                 Id = phone.Id,
                 Name = phone.Name,

PhoneStore/PhoneStore.csproj

@@ -20,8 +20,4 @@
       <_ContentIncludedByDefault Remove="wwwroot\Files\book.pdf" />
     </ItemGroup>
 
-    <ItemGroup>
-      <Folder Include="Pages" />
-    </ItemGroup>
-
 </Project>

PhoneStore/ViewModels/PhoneViewModels/IPhoneEditable.cs

+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using PhoneStore.Models;
+
+namespace PhoneStore.ViewModels.PhoneViewModels
+{
+    public interface IPhoneEditable
+    {
+        public int Id { get; set; }
+        [Required(ErrorMessage = "Поле обязательно для заполнения")]
+        [Remote("CheckName", "PhoneValidator", ErrorMessage = "Имя занято", AdditionalFields = nameof(Id))]
+        [StringLength(50, MinimumLength = 3, ErrorMessage = "Минимальная длина 3 символа, максимальная - 50")]
+        public string Name { get; set; }
+        [Required(ErrorMessage = "Поле обязательно для заполнения")]
+        [Range(1000, 50000, ErrorMessage = "Значение не валидно, вводить можно знаение от 1000 до 5000")]
+        public decimal? Price { get; set; }
+        public int BrandId { get; set; }
+        public List<Brand> Brands { get; set; }
+        public IFormFile File { get; set; }
+        public string Image { get; set; }
+    }
+}
\ No newline at end of file

PhoneStore/ViewModels/PhoneViewModels/PhoneCreateViewModel.cs

@@ -6,7 +6,7 @@ using PhoneStore.Models;
 
 namespace PhoneStore.ViewModels.PhoneViewModels
 {
-    public class PhoneCreateViewModel : BaseEntity
+    public class PhoneCreateViewModel : BaseEntity, IPhoneEditable
     {
         [Required(ErrorMessage = "Поле обязательно для заполнения")]
         [Remote("CheckName", "PhoneValidator", ErrorMessage = "Имя занято")]

PhoneStore/ViewModels/PhoneViewModels/PhoneEditViewModel.cs

+using System.Collections.Generic;
+using Microsoft.AspNetCore.Http;
+using PhoneStore.Models;
+
+namespace PhoneStore.ViewModels.PhoneViewModels
+{
+    public class PhoneEditViewModel : BaseEntity, IPhoneEditable
+    {
+        public string Name { get; set; }
+        public decimal? Price { get; set; }
+        public int BrandId { get; set; }
+        public List<Brand> Brands { get; set; }
+        public IFormFile File { get; set; }
+        public string Image { get; set; }
+    }
+}
\ No newline at end of file

PhoneStore/Views/Phones/About.cshtml

 @using PhoneStore.Repositories.Interfaces
 @using Microsoft.AspNetCore.Identity
-@model PhoneStore.ViewModels.PhoneViewModels.PhoneViewModel
-@inject IFeedbackRepository _feedbackRepository;
-@inject UserManager<User> _userManager;
+@model PhoneViewModel
+@inject IFeedbackRepository FeedbackRepository;
+@inject UserManager<User> UserManager;
 @{
     ViewBag.Title = "Подробная информация";
     Layout = "_Layout";
@@ -18,7 +18,7 @@
         </div>
         @if (User.Identity.IsAuthenticated)
         {
-            if (!_feedbackRepository.CheckFeedbackExists(int.Parse(_userManager.GetUserId(User)), Model.Id))
+            if (!FeedbackRepository.CheckFeedbackExists(int.Parse(UserManager.GetUserId(User)), Model.Id))
             {
                 <form class="mb-3" id="feedbackForm">
                     <div class="form-group">

PhoneStore/Views/Phones/Create.cshtml

-@model PhoneStore.ViewModels.PhoneViewModels.PhoneCreateViewModel
+@model IPhoneEditable
 
 @{
     ViewBag.Title = "title";

PhoneStore/Views/Phones/Edit.cshtml

-@model PhoneStore.ViewModels.PhoneViewModels.PhoneCreateViewModel
+@model IPhoneEditable
 
 @{
     ViewBag.Title = "Редактирование";

PhoneStore/Views/Phones/Index.cshtml

@@ -4,7 +4,7 @@
     ViewBag.Title = "Смартфоны";
     Layout = "_Layout";
 }
-@if (Model.Phones.Count() == 0)
+@if (!Model.Phones.Any())
 {
     <h2>Список пуст.</h2>
 }

PhoneStore/Views/Phones/PartialViews/PhoneFormPartialView.cshtml

-@model PhoneStore.ViewModels.PhoneViewModels.PhoneCreateViewModel
+@model PhoneStore.ViewModels.PhoneViewModels.IPhoneEditable
 <div class="mb-3">
     <label asp-for="Name" class="form-label">Наименование</label>
     <input type="text" class="form-control" asp-for="Name">

PhoneStore/Views/Shared/PartialViews/FeedbackPartialView.cshtml

 @using Microsoft.AspNetCore.Identity
-@model PhoneStore.ViewModels.Feedback.FeedbackViewModel
+@model FeedbackViewModel
 @inject UserManager<User> UserManager;
 
 <div id="@Model.Id" class="card mb-3">

PhoneStore/Views/_ViewImports.cshtml

@@ -2,4 +2,6 @@
 @using PhoneStore.Models
 @using PhoneStore.ViewModels
 @using PhoneStore.ViewModels.Account
+@using PhoneStore.ViewModels.PhoneViewModels
+@using PhoneStore.ViewModels.Feedback
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
\ No newline at end of file