[susan53]

First of all the grammar. It should be : The phone has broken down
To break down can only be used as an active verb - not passive. here, you're describing a past event with a present result - so you need the present perfect : auxiliary HAVE + past participle of the main verb.

As I said before Break down is used with mechanical and technological objects - the car has broken down / the computer has broken down - and means is not working at all.

But think about a telephone - if you can't make a telephone call, the problem is probably not with the telephone itself, but with the telephone line. So you'd say : The phone isn't working or The phone is out of order meaning there's something wrong somewhere. You couldn't say The phone has broken down because it's not a mechanical problem with the telephone itself.