I need help to translate these sentences in the past tense.

What did you talk about?
Did you go to sleep when you got off the phone?
How long was you on the phone for?

You don't state if you are using the familiar (tú) or the formal (Usted), singular or plural. Here is the familiar singular:

¿De qué hablaste?
¿Te dormiste al colgar el teléfono? (upon hanging up)
the English is "How long WERE you on the phone?) = ¿Cuánto tiempo estuviste en el teléfono?

Sra