Here’s what Lockdown Mode on your iPhone does:
Message Attachments are blocked, except for images.
FaceTime calls, and other incoming invitations and service requests, from unknown callers are blocked.
Shared albums will be removed from the Photos app, and new invites are blocked.
You cannot connect to a computer through a wired connection.
If a corporate or school network send you a configuration profile to define settings, this will be blocked when iPhone is locked.
Do you have questions about Lockdown Mode? Let us know.
Sources: 9to5 Mac; Music by BenSound