Telefonul meu este pe biroul din dormitor.

Because Romanian usually puts the definite article at the end of the noun, instead of using a separate word like English the.

• telefon = phone

• telefonul = the phone

• birou = desk
• biroul = the desk

So in this sentence:

• telefonul meu = my phone / literally the phone my
• biroul = the desk

This is one of the biggest differences from English word structure.

In Romanian, possessive words like meu often come after the noun.

So:

• telefonul meu = my phone
• cartea mea = my book
• prietenii mei = my friends

This is the normal Romanian order. English says my phone, but Romanian says something more like phone-the my.

Also, when a noun has a possessive like meu, Romanian usually still keeps the definite article on the noun:

• telefonul meu = my phone
• not usually telefon meu

Because meu has to agree with the noun it describes.

Telefon is a masculine singular noun, so the correct form is meu.

Some common possessive forms are:

• masculine singular: meu
• feminine singular: mea
• masculine plural: mei
• feminine plural: mele

Examples:

• telefonul meu = my phone
• cartea mea = my book
• băieții mei = my boys
• cărțile mele = my books

So here, telefonul meu is correct because telefon is masculine singular.

Este means is. It is the 3rd person singular of a fi = to be.

So:

• Telefonul meu este pe biroul din dormitor.
• literally: My phone is on the desk in the bedroom.

In standard Romanian, you normally keep este in a sentence like this.

In everyday speech, people very often shorten it to e:

• Telefonul meu e pe biroul din dormitor.

That sounds natural and common.

Here, pe means on.

So:

• pe birou = on the desk
• pe masă = on the table
• pe pat = on the bed

So este pe biroul means is on the desk.

A small warning: pe has other uses in Romanian too, especially with direct objects referring to people, but in this sentence it is simply the preposition on.

Because the sentence means the desk, not just a desk or desk.

• birou = a desk / desk
• biroul = the desk

So:

• pe birou = on a desk / on the desk, depending on context
• pe biroul = clearly on the desk

In this sentence, the speaker is referring to a specific desk, so the definite form biroul is used.

This is a very common learner question.

By itself:

• în dormitor usually means in the bedroom
• din dormitor usually means from the bedroom

But in a phrase like biroul din dormitor, din is often used to connect one noun to another and identify which one you mean:

• biroul din dormitor = the desk in the bedroom

So here din dormitor describes biroul. It tells you which desk: the one located in the bedroom.

Romanian often uses din in this kind of noun phrase where English would naturally say in.

Because din dormitor is a normal, natural phrase in Romanian here.

In this sentence:

• biroul din dormitor = the desk in the bedroom

The noun dormitor can stay without the definite article in this type of expression.

You can sometimes hear or use definite forms after prepositions in other contexts, especially when the noun is more specifically identified:

• din dormitorul meu = from/in my bedroom
• din dormitorul mare = from/in the big bedroom

But in the sentence you were given, din dormitor is the natural standard phrasing.

Romanian word order is more flexible than English word order, but this sentence uses the most neutral, standard order:

• Telefonul meu este pe biroul din dormitor.

You may also hear:

• Telefonul meu e pe biroul din dormitor.
• Pe biroul din dormitor este telefonul meu.

The second version puts more focus on the location.

So yes, Romanian can move things around for emphasis, but the original sentence is the most straightforward one for a learner to use.

You would use the indefinite form.

• telefon = phone
• un telefon = a phone

Examples:

• Un telefon este pe birou. = A phone is on the desk.
• Telefonul este pe birou. = The phone is on the desk.
• Telefonul meu este pe birou. = My phone is on the desk.

Notice that with my phone, Romanian normally uses the definite noun:

• telefonul meu not usually
• un telefon meu

Yes. E is the short, very common spoken form of este.

So both are correct:

• Telefonul meu este pe biroul din dormitor.
• Telefonul meu e pe biroul din dormitor.

The version with este may sound a bit more careful or formal, while e is extremely common in everyday conversation.

It describes biroul, not telefonul.

So the structure is:

• Telefonul meu = the subject
• este = is
• pe biroul din dormitor = on the desk in the bedroom

More specifically:

• biroul din dormitor = the desk in the bedroom

So the meaning is not that the phone is somehow from the bedroom by itself; rather, it is on the desk that is in the bedroom.