Telefone was marked incorrect for me, but telefone is the imperative in você form, so should this also be a correct answer?
Ah it must be conjugated for "tu", not "você". I didn't think of that. Thanks Paulo.
it's strange. We use "tu" instead of "você" but for imperative and object pronouns we usually use the form conjugated for "tu" :S
It has a different meaning, but as we have no context, it should also be accepted. But in this case you don't need a preposition:
Chama ele (informal) / Chama-o/Chame-o (formal).
Some verbs in Portuguese require preposition, while in English they don't, and vice-versa.
Listen TO the music = escute a música (Portuguese verb requires no preposition here.)
Call him = Ligue para ele (Portuguese verb requires preposition, while in English you don't use it.)
Another case of various meanings. Phone her is specific, call her is not. I would just yell, for example "CHILDREN, LUNCH IS READY". Is Ligar or chame-a better choice?
Here, it means "to phone", like "ligue para ele".
For the latter option, it would be "Chame-o".