Learn Hardcore Russian: Перед сном стоит выключить телефон. - Before going to sleep, it’s worth turning off the phone.

Here стоит + infinitive is an impersonal recommendation meaning it’s worth / it’s a good idea / one should. It comes historically from стоить (to be worth), not стоять (to stand).
So Перед сном стоит выключить телефон = Before going to sleep, it’s a good idea to turn off the phone.

Why is there no subject like you or we in the sentence?

Russian often uses impersonal structures for general advice. Стоит + infinitive doesn’t need an explicit subject; it’s understood as in general / for anyone / for you depending on context.
If you want to name the person, you can add a dative pronoun:

Тебе стоит выключить телефон перед сном. = You should turn off your phone before sleep.

Why is it перед сном and not перед сон or something else? What case is сном?

Перед (before/in front of) requires the instrumental case.

сон (sleep) → instrumental сном
So перед сном literally means before sleep / prior to sleeping.

Is перед сном the same as перед тем как лечь спать?

They’re close, but not identical in style and precision:

перед сном = before sleep / before going to bed (short, common, slightly more general)
перед тем как лечь спать = before (you) lie down to sleep (more explicit, more “action-based”)
Both can work in many contexts.

Why is the verb выключить (perfective) and not выключать (imperfective)?

Выключить is perfective and focuses on a single completed action: turn it off (once). That’s the normal choice for advice like this.
Выключать (imperfective) would suggest a repeated habit or process:

Перед сном стоит выключать телефон. = It’s a good idea to (habitually) turn off the phone before sleep.

Could I replace стоит with нужно, надо, or следует? What’s the difference?

Yes, but the strength and tone change:

стоит = mild, polite recommendation (it’s worth / it’s a good idea)
надо / нужно = stronger necessity (need to / have to)
следует = more formal, “should” in instructions/rules
So Перед сном стоит выключить телефон sounds like friendly advice rather than a strict requirement.

Does выключить телефон definitely mean powering the phone off, or can it mean turning off sound?

By default, выключить телефон most naturally means turn the phone off (power down).
If you mean sound/notifications, Russian usually specifies it:

выключить звук = turn off the sound
поставить на беззвучный = put on silent
отключить уведомления = disable notifications

Why is the word order like this—Перед сном стоит выключить телефон—and can it be rearranged?

Russian word order is flexible. This version puts the time phrase first, setting the context. Common alternatives:

Стоит выключить телефон перед сном. (neutral)
Перед сном телефон стоит выключить. (more emphasis on телефон)
All are grammatical; the choice is mostly about emphasis and rhythm.

Is it okay to omit перед сном and just say Стоит выключить телефон?

Yes. Then it becomes a general suggestion without the timing detail: It’s a good idea to turn off the phone.
Adding перед сном narrows it to that specific situation.

How do I say this directly to someone (like an instruction), not as general advice?

For a direct instruction you’d usually use the imperative:

Перед сном выключи телефон. (informal singular: “you”)
Перед сном выключите телефон. (polite / plural)
Those sound more like telling someone what to do, not merely suggesting.

What are the stress patterns and pronunciation points I should know?

перед: stress on the second syllable: пе-РЕД
сном: single syllable, pronounced like snom (with o reduced slightly)
стоит: сто-ИТ
выключить: ВЫ-клю-чить (stress on вы)
телефон: те-ле-ФОН

Is телефон here “telephone” (landline) or “mobile phone”?

In modern everyday Russian, телефон commonly means mobile phone unless context clearly indicates a landline. If you want to be explicit:

мобильный телефон or смартфон (smartphone)