Learn Hardcore Czech: Nevím, kde je můj telefon. - I don't know where my phone is.

So the comma simply marks the boundary between the main clause and the subordinate clause. Unlike English, where you might write “I don’t know where my phone is” without a comma, Czech orthography requires it here.

Why is the word order kde je můj telefon and not something like kde můj telefon je?

Both kde je můj telefon and kde můj telefon je are grammatically possible, but they feel different:

kde je můj telefon – the most natural, neutral word order, and what people usually say.
kde můj telefon je – marked/emphatic word order. It puts more emphasis on můj telefon, often sounding a bit dramatic or contrastive:
“where my phone is (as opposed to something/someone else’s).”

Also, compare:

Direct question: Kde je můj telefon? – “Where is my phone?”
Indirect question: Nevím, kde je můj telefon. – “I don’t know where my phone is.”

Notice that Czech keeps (almost) the same word order in the indirect question as in the direct question. English changes from “Where is my phone?” (direct) to “I don’t know where my phone is” (indirect). Czech does not make that change; it basically just embeds the question as it is.

Why do we say můj telefon and not svůj telefon?

The choice between můj and svůj in Czech depends on who the subject of the clause is.

můj = my
svůj = “one’s own” (reflexive; must refer back to the subject of the same clause)

In kde je můj telefon, the verb je has the subject telefon. So in that clause, the subject is telefon, not “I”.

If you said kde je svůj telefon, Czech grammar would interpret svůj as referring to the subject of that clause, i.e. to telefon. That would mean something like “where its own phone is” – which doesn’t make sense.

So:

✅ Nevím, kde je můj telefon. – correct: “I don’t know where my phone is.”
❌ Nevím, kde je svůj telefon. – ungrammatical / nonsensical: suggests “where its own phone is.”

You can only use svůj when the possessor is the subject of the same clause:

Mám svůj telefon. – “I have my (own) phone.” (subject “I” → possessor “I”)

What case is můj telefon in here, and why?

Můj telefon is in the nominative case.

Reason: in the clause kde je můj telefon, the verb je (“is”) works like the English linking verb “to be.” It connects the subject and a complement that is also in the nominative:

Telefon je nový. – “The phone is new.”
To je můj telefon. – “That is my phone.”
kde je můj telefon – “where my phone is”

So:

telefon = subject (nominative)
můj agrees with telefon → also nominative (masculine inanimate, singular: můj)

Could I drop můj and just say Nevím, kde je telefon?

Yes, you can.

Nevím, kde je telefon. – “I don’t know where the phone is.”

Whether you need můj depends on context:

If it’s obvious you’re talking about your own phone, people will understand Nevím, kde je telefon as “I don’t know where my phone is.”
If there are several phones and you need to distinguish yours from others, you’d keep můj:
Nevím, kde je můj telefon. – “I don’t know where my phone is (as opposed to yours/the office phone/etc.).”

You can even say ten můj telefon for extra emotional emphasis:

Nevím, kde je ten můj telefon.
roughly: “I don’t know where that damn phone of mine is.” (depends on tone)

What’s the difference between Nevím, kde je můj telefon and Nevím, kde mám telefon?

Both are understandable and can be translated as “I don’t know where my phone is,” but there’s a nuance:

Nevím, kde je můj telefon.
– Neutral: you literally don’t know the location of your phone.
Nevím, kde mám telefon.
– Very common in speech. Often implies: “I don’t know where I (have) put my phone” or “I don’t know where I’m keeping my phone.”
– The verb mám (“I have”) suggests your relationship to the object (“where I have it / keep it”) rather than just “where it exists.”

In everyday conversation, you’ll frequently hear Nevím, kde mám telefon, especially when someone is searching for their misplaced phone.

Do I need to say já? Is Já nevím, kde je můj telefon more correct?

You don’t need já here. In Czech, the verb ending already shows the person:

nevím → 1st person singular (“I don’t know”)

So:

Nevím, kde je můj telefon. – perfectly normal, default version.
Já nevím, kde je můj telefon. – also correct, but já adds emphasis:
“I don’t know where my phone is” (maybe someone else knows, or you’re stressing your own ignorance).

Use já when you want to emphasize the subject; otherwise you typically omit it.

How is nevím related to the infinitive vědět? Why not something like vědím?

The verb vědět (“to know”) is irregular; you can’t form the present tense by just adding normal endings to věd-.

The present tense of vědět:

(já) vím – I know
(ty) víš – you know
(on/ona/to) ví – he/she/it knows
(my) víme – we know
(vy) víte – you (pl./formal) know
(oni) vědí / ví – they know (both forms used)

Negation is formed by adding ne- in front:

nevím – I don’t know
nevíš – you don’t know
neví – he/she/it/they don’t know, etc.

So nevím literally is “not-know-I.”

How do you pronounce Nevím, kde je můj telefon?

Approximate pronunciation (in simplified English-like terms):

Nevím – NEH-veem
- e as in “get”
- í is a long ee sound
kde – gdeh
- The k is actually pronounced, but kde comes out very quickly, almost like “gdeh” for English ears.
je – yeh
můj – roughly mooy
- Czech ůj is a diphthong, like a long oo plus y at the end.
telefon – TEH-le-fon
- Stress is always on the first syllable in Czech: NE-vím, KDE je MŮJ TE-le-fon.

So the whole sentence:
NE-vím, kde je můj TE-le-fon.

Can I change the clause order, like Kde je můj telefon, nevím?

Yes, that word order is grammatically possible, but it’s unusual and stylistically marked.

Nevím, kde je můj telefon. – normal, neutral.
Kde je můj telefon, nevím. – sounds literary/poetic or very emphatic. You’d be more likely to see this in written stylistic text or for dramatic effect, not in everyday speech.

In regular conversation, stick with Nevím, kde je můj telefon.