"Estou de volta."
This translates literally to "I am of return".
Here are some other options, depending on the context:
* "Voltei." (I returned) - This is more succinct and can be used when the focus is on the action of returning.
* "Já estou de volta." (I am already back) - This emphasizes that you have already returned.
* "Voltei para [place]." (I returned to [place]) - This specifies where you returned to.
Example sentences:
* "Estou de volta da viagem." (I'm back from the trip.)
* "Voltei para casa." (I returned home.)
* "Já estou de volta, pode começar." (I'm back, you can begin.)