Translation:The phone is broken
Phasal verb such as "break down" and compound verbs are very common in English and other indo-european languages, in many cases they may translate word for word between languages in the group because the origin is from an older common root. Eg "overnight-över natten-ubernacht-..." although I don't think this is the case with "broken down"? Swahili is Bantu, phasal verbs are not going to translate word for word unless the phasal verb is loaned from another language.
In Swahili, there is no separate grammar/distinction for those two. Generally, you would always translate it as "is broken" as something that has been broken is now in the state of being broken - this applies to a couple more words. (like sit = have sat down or stand = have stood up)
And I'll add my voice to the chorus that it is still in beta, there are other resources out there for complementation and you could either wait til it is complete or help out practically if it really annoys you so much (sorry, I'm annoyed with all the complaints on here, as well) - then you would see more comments where people put recommendations on how to get around it and report etc.