<Page.BottomAppBar>

        <CommandBar x:Name="mainCommandBar" Visibility="Visible"  >

            <CommandBar.SecondaryCommands>

                <AppBarButton x:Name="btnAbout" Label="About" Click="btnAbout_Click" />

                <AppBarButton x:Name="btnRate" Label="Rate" Click="btnRate_Click" />

            </CommandBar.SecondaryCommands>

        </CommandBar>

    </Page.BottomAppBar>

Se si vuole visualizzare in formato Compresso su WP, allora inserire il seguente codice in C#

#if WINDOWS_PHONE_APP

            mainCommandBar.ClosedDisplayMode = AppBarClosedDisplayMode.Minimal;

#endif