Вы можете позвонить мне когда угодно, если у Вас есть вопрос.

In this sentence, Вы and Вас are written with a capital letter to show politeness and formality.

Russian has:

• ты = informal you (singular)
• вы = plural you, and also formal/polite you for one person

In formal writing, people sometimes capitalize these forms:

• Вы
• Вас
• Вам

So если у Вас есть вопрос sounds polite, like speaking to a client, student, or someone you do not know well.

In modern Russian, lowercase вы / вас is also very common, even when speaking politely. The capital letter adds extra formality or respect.

Russian often uses a structure like:

• мочь + infinitive = can / may + verb

So:

• Вы можете позвонить = You can call

Here:

• можете = can / may (2nd person plural/formal singular)
• позвонить = to call by phone

This is very natural in Russian. It makes the sentence sound polite and non-pushy: You may call me...

Because the verb позвонить takes the dative case, not the accusative.

The pattern is:

• позвонить кому? = to call whom?

So:

• мне = dative of я
• Вам = dative of Вы

Examples:

• Позвоните мне. = Call me.
• Я позвоню маме. = I’ll call Mom.

English says call me, but Russian grammar treats it more like call to me, so it uses the dative.

This is an aspect question.

• звонить = imperfective
• позвонить = perfective

In this sentence, позвонить is used because it refers to a single completed phone call: you may call me at any time.

Compare:

• Вы можете позвонить мне. = You can give me a call.
• Вы можете звонить мне каждый день. = You can call me every day.

So:

• позвонить = one call / completed action
• звонить = repeated action, process, or general activity

Когда угодно means any time, whenever you like, or at any time at all.

It is a fixed expression:

• когда = when
• угодно = literally something like it is pleasing / desired, but in this expression you should learn it as one unit

Common similar expressions:

• где угодно = anywhere
• кто угодно = anyone
• что угодно = anything

So позвонить мне когда угодно means to call me whenever you want.

Because когда угодно here is a set expression, not a full subordinate clause.

So:

• Вы можете позвонить мне когда угодно = no comma

But there is a comma before если, because если у Вас есть вопрос is a real subordinate clause:

• ..., если у Вас есть вопрос.

So the comma is there because of если, not because of когда.

Russian usually expresses possession with:

• у + genitive + есть

So:

• у Вас есть вопрос = literally at you there is a question
• natural English meaning: you have a question

This is the normal way to say have in many situations.

The verb иметь does exist and means to have, but it is used less often in everyday speech and can sound more formal, bookish, or specialized.

So in ordinary conversation:

• У меня есть машина. = I have a car.
• У Вас есть вопрос. = You have a question.

After the preposition у, Russian uses the genitive case.

So:

• Вы = nominative
• Вас = genitive / accusative form

In у Вас есть вопрос, Вас is genitive because у requires it.

This whole pattern means possession:

• у меня есть... = I have...
• у тебя есть... = you have...
• у него есть... = he has...
• у Вас есть... = you have... (formal)

Russian has no articles like a or the.

So вопрос can mean:

• a question
• the question

You understand which one is meant from context.

In this sentence, если у Вас есть вопрос most naturally means if you have a question / any question.

That indefinite meaning comes from the context, not from an article.

Yes. Russian word order is more flexible than English.

This sentence could also be:

• Если у Вас есть вопрос, Вы можете позвонить мне когда угодно.

That version puts the condition first: If you have a question...

You could also hear:

• Вы можете мне позвонить когда угодно, если у Вас есть вопрос.

The meaning stays basically the same. The differences are mostly about focus, rhythm, and style, not grammar.

It is polite and fairly formal, mainly because of:

• Вы
• Вас
• the overall phrasing

It sounds appropriate in situations like:

• teacher to student
• customer support
• doctor to patient
• colleague to colleague in a professional setting

If you were speaking to a close friend, you would probably use ты instead:

• Ты можешь позвонить мне когда угодно, если у тебя есть вопрос.

That is the informal version.