Я спросил у продавца, будет ли этот телефон в наличии завтра.

Спросил is the perfective past of спросить, so it means I asked as a completed action.

• я спросил = I asked once / I asked and got the question out
• я спрашивал = I was asking / I asked repeatedly / I used to ask

In this sentence, the speaker is referring to one completed act of asking the salesperson, so спросил is the natural choice.

Russian often uses спросить у + genitive for ask someone.

So:

• спросить у продавца = to ask the salesperson
• literally, something like ask from the salesperson

This is a very common pattern:

• спросить у мамы
• спросить у друга
• спросить у учителя

You may also see спросить продавца, which is possible in some contexts, but спросить у продавца is a very standard and clear way to say ask the salesperson.

Because у requires the genitive case.

The dictionary form is продавец.
After у, it becomes продавца.

So:

• продавец = salesperson
• у продавца = from / with the salesperson

This is just normal case government:

• у брата
• у сестры
• у учителя
• у продавца

In indirect yes/no questions, ли usually comes after the first word or phrase being questioned.

Here, the questioned element is будет:

• будет ли этот телефон в наличии завтра = whether this phone will be in stock tomorrow

So ли follows будет.

This is a very common pattern:

• Я не знаю, придёт ли он.
• Спроси, можно ли войти.
• Интересно, будет ли дождь.

Putting ли before будет would be ungrammatical in standard Russian.

Ли marks an indirect yes/no question. In English, it often corresponds to whether or sometimes if.

So:

• будет ли этот телефон... = whether this phone will be...

Compare:

• direct question: Этот телефон будет в наличии завтра?
• indirect question: Я спросил, будет ли этот телефон в наличии завтра.

So ли is one of the main signals that the clause is not a statement, but an embedded yes/no question.

Because если usually means if in the sense of on the condition that, not whether.

Compare:

• Я спросил, будет ли этот телефон в наличии завтра.
  = I asked whether this phone would be in stock tomorrow.

• Если этот телефон будет в наличии завтра, я его куплю.
  = If this phone is in stock tomorrow, I’ll buy it.

So here you need ли, not если, because the sentence is about a question, not a condition.

В наличии means in stock, available, or available for purchase / on hand.

It is a very common shop and business expression.

Examples:

• Товар есть в наличии. = The item is in stock.
• Сейчас нет в наличии. = It is currently out of stock.
• Будет в наличии завтра? = Will it be in stock tomorrow?

This phrase is fixed enough that learners often memorize it as a chunk: быть в наличии.

Because телефон is masculine singular nominative, and этот has to agree with it.

Agreement in Russian means the demonstrative matches the noun in:

• gender
• number
• case

So:

• этот телефон = this phone
• эта книга = this book
• это окно = this window
• эти телефоны = these phones

Here, телефон is the subject of будет, so it stays in the nominative case: этот телефон.

Because the subject is singular: этот телефон.

Russian verbs in the past and future agree with the subject in number, and sometimes gender in the past.

Here:

• телефон = singular
• therefore будет = singular future of быть

If the subject were plural, you would get:

• будут ли эти телефоны в наличии завтра?

Because the sentence has two clauses:

1. Я спросил у продавца
2. будет ли этот телефон в наличии завтра

The second clause is a subordinate clause explaining what was asked, so Russian separates it with a comma.

This is very common:

• Я знаю, что он дома.
• Я спросил, придёт ли она.
• Он сказал, что занят.

Yes, Russian word order is flexible, but not all changes are equally natural.

The most neutral version here is:

• Я спросил у продавца, будет ли этот телефон в наличии завтра.

You could also hear:

• Я спросил у продавца, будет ли завтра этот телефон в наличии.
• Я у продавца спросил, будет ли этот телефон в наличии завтра.

These alternatives may shift emphasis slightly, but the original is the most straightforward and natural for a learner to model.

One thing that generally does not change is the position of ли: it still follows the word being questioned.

Because that is a very natural place for a time expression in Russian, especially when it modifies the whole situation.

• будет ли этот телефон в наличии завтра

The sentence is asking about availability tomorrow, so завтра comes at the end as a simple time adverb.

Russian could move it for emphasis:

• будет ли завтра этот телефон в наличии
• завтра будет ли этот телефон в наличии — much less neutral

But the original order sounds natural and standard.

Very close, but Russian builds it differently.

English:

• I asked whether this phone would be in stock tomorrow.

Russian:

• Я спросил..., будет ли этот телефон в наличии завтра.

The main differences are:

• Russian uses ли to mark whether
• Russian keeps a more statement-like word order than English in some cases
• Russian uses будет because it is talking about future availability from the speaker’s past point of view

So the structure is not word-for-word identical to English, but the function is the same.

Normally, будет ли is better here because the question is about tomorrow, a future time.

• будет ли = will it be
• есть ли = is it

So:

• Есть ли этот телефон в наличии сейчас? = Is this phone in stock now?
• Будет ли этот телефон в наличии завтра? = Will this phone be in stock tomorrow?

Using есть ли with завтра would usually sound wrong or at least unnatural, because есть refers to present existence/availability, not future availability.

Not necessarily. Спросил only tells us that the speaker asked. It does not by itself say whether the salesperson answered, or what the answer was.

If you wanted to say that the speaker found out, Russian would use something else, for example:

• Я узнал у продавца... = I found out from the salesperson...
• Я спросил у продавца, и он сказал, что... = I asked the salesperson, and he said that...

So спросил focuses on the act of asking, not the result.