kaigi ga hazimaru mae ni, sumaho wo muon ni site kudasai.

が marks 会議 as the thing that begins.

• 会議が始まる = the meeting begins
• 会議は始まる would sound more like as for the meeting, it begins and would usually be used when contrasting it with something else or when the meeting is already the topic.

In this sentence, 会議が始まる前に is a straightforward clause meaning before the meeting begins, so が is the most natural choice.

When a verb comes before 前に, it usually stays in the plain/dictionary form if the action is still in the future relative to the main action.

So:

• 会議が始まる前に = before the meeting begins

This is the normal pattern:

• V-plain + 前に = before doing V / before V happens

Examples:

• 寝る前に = before going to bed
• 食べる前に = before eating

前 means before or in front, depending on context. Here it means before, and に marks the point in time.

So:

• 会議が始まる前に = before the meeting begins

It tells you the requested action should happen earlier than the meeting’s start.

This is because 始まる is an intransitive verb and 始める is a transitive verb.

• 始まる = to begin, to start
• 始める = to start something

Here, the meeting itself is the thing that begins:

• 会議が始まる = the meeting begins

If you used 始める, you would need someone to start it:

• 司会者が会議を始める = the chairperson starts the meeting

を marks the direct object of the action.

Here, the action is 無音にして from 無音にする, which means to make silent / to set to silent mode.

So:

• スマホを無音にする = to make the smartphone silent

The phone is the thing being changed, so it takes を.

This uses the pattern:

• noun + にする = make something into X / set something to X

So:

• 無音 = silence / mute
• 無音にする = make it silent, set it to mute

In this sentence:

• スマホを無音にしてください = please set your phone to silent

This same pattern is very common:

• 部屋をきれいにする = make the room clean
• 設定をオンにする = turn the setting on

They are actually the same thing.
無音にしてください is made from:

• 無音にして = te-form of 無音にする
• ください = please do

Together, 〜てください is the standard way to make a polite request:

• してください = please do

So:

• スマホを無音にしてください = please make your phone silent

Close, but not always exactly the same in every situation.

無音 literally means no sound or mute. In everyday device language, Japanese speakers might also say:

• マナーモードにしてください = please put it on manner mode / silent mode
• サイレントモードにしてください = please put it on silent mode

Your sentence is understandable and natural enough, but マナーモード is also very common when talking about phones in Japan.

It is a polite request.

• して alone can sound casual or blunt depending on context.
• してください is the standard polite form: please do.

So this sentence sounds appropriate for announcements, signs, workplaces, or formal instructions:

• 会議が始まる前に、スマホを無音にしてください。

It is polite, but still direct enough to function as an instruction.

Yes. That is a very natural English equivalent.

The Japanese sentence is essentially:

• Before the meeting begins, please set your smartphone to silent.

Depending on context, English might say:

• Please silence your phone before the meeting starts.
• Before the meeting starts, please put your phone on silent.

All of these match the Japanese well.

スマホ is a very common everyday word meaning smartphone. It is a shortened form of スマートフォン.

Other options have slightly different nuances:

• スマホ = smartphone, casual and very common
• スマートフォン = full form, a bit more formal or technical
• 携帯電話 = mobile phone / cell phone, broader and slightly more formal
• 電話 = phone, very general

In modern daily Japanese, スマホ is extremely common.

In normal Japanese writing, it would usually be written without spaces:

会議が始まる前に、スマホを無音にしてください。

The spaces in your version are just there to help learners read the parts more easily.

Yes. That is a very useful way to understand it.

前 is a noun meaning front or before. It can combine with clauses:

• 会議が始まる前 = the time before the meeting begins

Then に marks that time point:

• 会議が始まる前に = before the meeting begins

This is similar to other time nouns:

• 後に = after
• 時に = at the time when
• 前に = before

So yes, 前 behaves like a noun in this structure.