Update string to be phone/tablet agnostic

    <string name="notification_conversation_summary_low">No sound or vibration and appears lower in conversation section</string>

    <!-- [CHAR LIMIT=150] Notification Importance title: normal importance level summary -->

    <string name="notification_channel_summary_default">May ring or vibrate based on phone settings</string>

    <string name="notification_channel_summary_default">May ring or vibrate based on device settings</string>

    <!-- [CHAR LIMIT=150] Notification Importance title: high importance level summary -->

    <string name="notification_channel_summary_high">When device is unlocked, show notifications as a banner across the top of the screen</string>