>SMS and phone calls should never let the server see every file on your device,

That may be the case but the bug could still be on the server side:

  Carol the Client: Hi Steve, will you send this photo to 111-1111?

  Steve the Server: Hi Carol, I've sent your photo to 555-5555

Unless you encrypt the data to your recipient's client-side held key, the opportunity for the server to err and data leak, persists.

That doesn't explain the case where all photos on the phone were silently sent to a contact.