sensei ha denwa de youken dake saki ni hanasimasu to iimasita.

は marks 先生 as the topic: As for the teacher, ...

In a sentence like this, は feels natural because the teacher is already the person being talked about. The sentence is not mainly introducing who said it; it is mainly telling us what the teacher said.

If you used が, it would put more focus on the teacher as the one who said it, as if answering Who said that?

電話で means by phone / over the phone.

The particle で often marks the means or method used to do something.
So here:

• 電話で話します = speak by phone
• literally, use the phone as the means of speaking

This is different from 電話に, which would not work here for the same meaning.

用件 means business, matter, reason for contacting someone, or what you need to say.

It is often used in practical situations, especially when you want to get to the point.
So 用件だけ suggests something like:

• just the main point
• only the necessary business
• just what I need to say

It sounds a bit more practical and businesslike than a casual word like 話.

だけ means only / just.

So 用件だけ means:

• only the matter itself
• just the main point
• nothing beyond the necessary business

It limits what will be talked about. The nuance is that the speaker will not go into extra details, small talk, or other topics.

先に means first, before that, or ahead of other things.

In this sentence, it means the speaker will talk about the important matter before anything else.
So the flow is something like:

• first say the main point on the phone
• then maybe discuss other things later

It does not just mean early in a time sense; it often means before the other step(s).

Because 先に is functioning adverbially: it tells us in what order the speaking happens.

• 先に話します = speak first
• 先 here is not the direct object of 話す

The particle に is commonly used in expressions about order and timing, such as:

• 先に行く = go first
• 先に食べる = eat first

So 先に is a set, natural way to say first.

This is very common in Japanese quoted speech.

• 言いました is past because the act of saying happened in the past.
• 話します stays in the form that was used inside the quoted content.

So the teacher said something like:

• 電話で用件だけ先に話します。

That quoted statement uses 話します, which is polite non-past. In quotes, Japanese usually keeps the original form of what was said.

Also, non-past 話します can mean:

• I will speak
• I speak

Here it most likely means I will speak / I'll tell you.

The と marks the content of what was said. It is the quotation particle.

So:

• X と言いました = said X

In this sentence, everything before と is the quoted statement:

• 電話で用件だけ先に話します = the thing the teacher said

You can think of it like English quotation marks or that, depending on translation. Japanese often does this without punctuation.

Grammatically, it looks like a quote introduced by と, but in English it could be translated either way depending on context.

Possible translations:

• direct-ish: The teacher said, “I’ll tell you just the main point first over the phone.”
• indirect-ish: The teacher said that he/she would first discuss only the main point by phone.

Japanese does not always sharply separate direct and indirect quotation the way English does. The important thing is that と marks the content that was said.

Most likely yes, but it is technically omitted inside the quote.

Japanese often leaves out subjects when they are clear from context. In this sentence, the natural reading is that the teacher said something equivalent to I will speak..., so the understood subject of 話します is the speaker inside the quote, namely the teacher.

But Japanese does not explicitly say 先生は電話で...話します inside the quoted part. It simply omits the subject because it is understood.

The listener is not stated because Japanese often omits information that the context already makes clear.

話します can mean speak, tell, or talk about, and the sentence does not explicitly name the person being told. In English, we often want an object like tell me or tell them, but Japanese frequently leaves that unsaid if it is obvious from the situation.

So the sentence focuses on:

• how: by phone
• what: only the main point
• when/in what order: first

not on to whom.

Because と does not match English that perfectly.

In this structure, と is the particle that marks quoted content. Depending on how you translate, English may use:

• quotation marks
• that
• or nothing at all

For example:

• The teacher said, “...”
• The teacher said that ...
• sometimes just The teacher said ...

So と is required in Japanese here, but it does not always become a visible separate word in English.

All three are possible dictionary-level translations, but in this sentence tell is often the most natural English choice.

That is because the phrase is about communicating 用件—the main matter or business—to someone. So in English we often say:

• I’ll tell you the main point first over the phone

rather than the more literal:

• I’ll speak the business first by phone

Japanese 話す is broader than English talk in some contexts, so translation depends on what sounds natural.

The exact order is not completely fixed, but the given order is natural.

Japanese word order is more flexible than English because particles show each part’s role. For example, these are also possible in the right context:

• 用件だけ先に電話で話します
• 先に用件だけ電話で話します

However, each order can slightly change emphasis or flow. The original sentence sounds smooth and easy to process:

1. 電話で = by phone
2. 用件だけ = only the matter itself
3. 先に = first
4. 話します = will talk / tell

So learners should treat the original as a very natural model.

Both 話します and 言いました are in polite -ます style.

This can happen for two reasons:

1. the overall narration is polite
2. the teacher’s original words were also spoken politely

Japanese often preserves the politeness level of quoted speech. So if the teacher said 話します, that politeness stays inside the quote.

This is one reason the sentence may feel very formal or respectful compared with casual speech.