Answer:
zu
Step-by-step explanation:
Das Telefon findet man _zu_ Hause.
If you are ''in'' Home, so I mean ''dativ'' =>it should be zu Hause
but if you are ''going to'' Home ( a movement to home) => it should be nach Hause
if you still don't understand, you have to read articles about ''difference between nach Hause and zu Hause'', it's important. I can help you on comments.
Hope this helps ^-^