Learn Hardcore Japanese: watasi ha tomodati to denwa de hanasimasu.

The particle は marks the topic (“as for me”), highlighting that the speaker is the one doing the talking. は often contrasts or frames the discussion. が would instead mark the subject in a neutral or new-information sense (“someone talks”), but here we want to set 私 as the known topic.

Why is と used after 友達, and what does it mean here?

The particle と after 友達 means “with.” It indicates accompaniment, so 友達と translates to “with a friend.” It’s different from the quoting use of と.

What is the function of で in 電話で? Why not use を?

The particle で marks the means or instrument (“by phone”). Since 話します is intransitive here (you “talk” rather than “talk something”), you use で to show how the action is performed. を would typically mark a direct object, which isn’t needed for “talk” in this context.

Why is the verb 話します in this particular form?

話します is the polite present/future form of 話す (to speak/talk). It’s neutral and appropriate for everyday conversation or formal contexts. You could switch to the plain form 話す, the past polite 話しました, or other tenses depending on context and politeness level.

Can we reorder 友達と and 電話で, or must they stay in this order?

Japanese word order is relatively flexible for adverbial phrases. Both 友達と電話で話します and 電話で友達と話します are natural and mean the same thing. Emphasis might shift slightly based on which comes first.

Is 私 always necessary at the beginning? Can it be dropped?

You can usually drop 私 if context makes it clear who is speaking. 友達と電話で話します still means “I’ll talk with a friend by phone.” Including 私 makes the subject explicit, which can be useful for clarity or contrast.

Could you say 電話を友達と話します instead?

No. 電話を話します is ungrammatical because you don’t “talk the phone”; you “talk by phone.” To express “use the phone” you’d say 電話をかけます, but to talk via phone you use 電話で話します.