"Maybe he is on the phone?"
Translation:Han kanske pratar i telefon?
The verb must come second. "Han" isn't a verb. Kanske is strange because although "maybe" isn't a word, kanske is made up from "kan" "ske" ("can" "happen") and so satisfies the V2 rule. (I'm pretty sure my explaination is correct but if not then I'm sure someone will correct me).