Why the include function is not including the navigational property of the model?

I have these 2 models:

Phones:

public class Phones
    {
        public int ID { get; set; }
        public string Model { get; set; }
        public string Manufacturer { get; set; } // e.g. XIAOMI, NOKIA, IPHONE    
        public int UserID { get; set; }
        public List<Users> Users { get; set; }
    }

Users:

 public class Users
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string CNIC { get; set; }
    }

Context model:

    public class UsersPhonesDBContext: DbContext
    {
        public DbSet<Users> Users { get; set; }
        public DbSet<Phones> Phones { get; set; }
    }

and controller:

        public ActionResult PhoneUsers()
        {
            Object ObjPhoneUsers = context.Phones.Include(phone => phone.Users).FirstOrDefault().Users ;

            return View(ObjPhoneUsers);
        }

And View:

    @model IEnumerable<PracticeEF.Models.Phones>

    <table>
    @foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Model)

        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Manufacturer)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.UserID)
        </td>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id=item.ID }) |
            @Html.ActionLink("Details", "Details", new { id=item.ID }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.ID })
        </td>
    </tr>
}

Problem:

The problem is that it returns the navigational property (Users list in Phones model) being empty. Even the records are filled and being mapped via the foreign key in the database but it doesn't pick any record of the user but only Phones.

Why?

Update:

I even tried this and returns nothing, nor the users nor the phones.

 public ActionResult PhoneUsers()
        {
            object ObjPhoneUsers = context.Phones.Where(x => x.Manufacturer == "Apple Inc").Include(x => x.Users).ToList();

            return View(ObjPhoneUsers);
        }