MainWindow.xaml

<Window x:Class="MVVM.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:MVVM"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Style TargetType="TextBlock">
            <Setter Property="FontSize" Value="14"/>
        </Style>
        <Style TargetType="TextBox">
            <Setter Property="FontSize" Value="14"/>
        </Style>
        <Style TargetType="Button">
            <Setter Property="Width" Value="40"/>
            <Setter Property="Margin" Value="5"/>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="0.8*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="0.2*"/>
        </Grid.RowDefinitions>
        
        <ListBox Grid.Column="0" ItemsSource="{Binding Phones}"
                 SelectedItem="{Binding SelectedPhone}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Margin="5">
                        <TextBlock FontSize="18" Text="{Binding Path=Title}"/>
                        <TextBlock Text="{Binding Path=Company}"/>
                        <TextBlock Text="{Binding Path=Price}"/>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <StackPanel Grid.Row="1" Orientation="Horizontal">
            <Button Command="{Binding AddCommand}">+</Button>
            <Button Command="{Binding RemoveCommand}"
                    CommandParameter="{Binding SelectedPhone}">-</Button>
        </StackPanel>

        <StackPanel Grid.Column="1" DataContext="{Binding SelectedPhone}">
            <TextBlock Text="Выбранный элемент"/>
            <TextBlock Text="Модель"/>
            <TextBox Text="{Binding Title, UpdateSourceTrigger=PropertyChanged}"/>
            <TextBlock Text="Производитель"/>
            <TextBox Text="{Binding Company, UpdateSourceTrigger=PropertyChanged}"/>
            <TextBlock Text="Цена"/>
            <TextBox Text="{Binding Price, UpdateSourceTrigger=PropertyChanged}"/>
        </StackPanel>
    </Grid>
</Window>