The group model

PhoneGroup.cs

public class PhoneGroup : ObservableCollection<Phone>
{
    public string Name { get; private set; }

    public PhoneGroup(string name)
        : base()
    {
        Name = name;
    }

    public PhoneGroup(string name, IEnumerable<Phone> source)
        : base(source)
    {
        Name = name;
    }
}