Learn Dutch: De baas roept ons. - The boss is calling us.

Ons means "us", which is the object form of wij or we (we). Since the boss is the one doing the calling, "us" is receiving the action, so you must use the object pronoun ons.

Wait, doesn't ons also mean "our"?

Yes, good catch! Ons is used as both the object pronoun "us" (like in this sentence) and the possessive pronoun "our" for het-words (like ons huis meaning "our house"). You can tell it means "us" here because it stands alone and isn't attached to a noun.

The translation says "is calling", but there is no Dutch word for "is" in the sentence. Why?

Dutch doesn't have a continuous "is doing" tense like English. The single present tense verb roept covers both "calls" and "is calling". You just choose which one makes the most sense in English based on the context.

Does roept mean calling on the telephone?

Not usually. The verb roepen means to call out, to shout, or to summon (like a boss calling you into their office). If the boss were calling you on the telephone, you would normally use the verb bellen.