Learn Finnish: Asiakaspalvelu on helppo tavoittaa puhelimitse. - The customer service is easy to reach by phone.

The prolative ending -tse is almost always attached to the plural stem of a word, even when the meaning is singular. For puhelin (phone), the basic stem is puhelime-, but the plural stem is puhelimi-. Adding -tse to the plural stem gives us puhelimitse (by phone or via phone).

Could I just say puhelimella instead of puhelimitse?

Yes, you can. Puhelimella (using the adessive case -lla/-llä) is the more common, everyday way to say you do something "by phone" or "with a phone". The prolative form puhelimitse means the exact same thing but is a bit more formal. It is heavily used in official contexts, business communications, and written Finnish.

Why is asiakaspalvelu in the nominative case instead of an object case, since it is the thing being reached?

This is a special sentence structure used with adjectives like helppo (easy) or vaikea (hard) followed by a verb in its basic dictionary form (tavoittaa). In this "X is easy to do" structure, the target of the action becomes the grammatical subject of the sentence. Because it acts as the subject, it stays in the basic nominative case (asiakaspalvelu) rather than taking an object case like the genitive asiakaspalvelun.

How does tavoittaa differ from other verbs that translate to "reach", like ?