"He does not have a phone."

Translation: On nie ma telefonu.

[Bryde6]

I didn't try it but does Duolingo accept using komórki (cell/mobile) as a right answer? In casual speak I don't think folks would say "he doesn't have a mobile". The generic "phone" no longer is attributed to "land line".
Dzienkuje

[Jellei]

We agree that "phone" and "mobile" usually mean the same nowadays. We accept "komórki" here.

Although frankly I think it makes more sense the other way round, accepting "telefon" when "komórka" would be expected.

[jamielniak]

Ele não tem um telefone