Το τηλέφωνό μου είναι κάτω από το κρεβάτι.

This is a common spelling feature in Modern Greek.

The basic word is το τηλέφωνο. But when a weak possessive like μου, σου, του, etc. comes after the noun, Greek often adds a second written stress mark if needed:

• το τηλέφωνο
• το τηλέφωνό μου

This helps show the correct rhythm and stress of the phrase. You will see this a lot with words stressed on the third-to-last syllable.

Compare:

• ο άνθρωπος
• ο άνθρωπός μου

So the extra accent is not changing the meaning; it is showing the correct pronunciation of the noun + possessive phrase.

In Greek, possessive words like μου usually come after the noun:

• το τηλέφωνό μου = my phone
• το βιβλίο μου = my book

This is one of the biggest differences from English. Greek often says literally:

• the phone my
• the bed my
• the house my

So το τηλέφωνό μου is the normal way to say my phone.

Because Greek normally keeps the definite article even with possession.

So where English says:

• my phone

Greek usually says:

• the phone my → το τηλέφωνό μου

This is completely normal Greek grammar. The article is not optional here in standard everyday Greek.

κάτω από means under, below, or beneath.

It is a two-word expression:

• κάτω = down / below
• από = from

But together, κάτω από functions like the English preposition under.

Examples:

• κάτω από το τραπέζι = under the table
• κάτω από την καρέκλα = under the chair
• κάτω από το κρεβάτι = under the bed

So in your sentence, κάτω από το κρεβάτι is the location phrase.

Because από takes the accusative case, and κρεβάτι is a neuter noun whose nominative and accusative singular forms are the same.

So:

• nominative: το κρεβάτι
• accusative: το κρεβάτι

There is no visible change here.

For comparison, with a masculine noun you would see a clearer difference:

• ο φίλος = the friend
• βλέπω τον φίλο = I see the friend

But with το κρεβάτι, the form stays το κρεβάτι.

Both are neuter nouns.

You can tell because they use the neuter article το:

• το τηλέφωνο
• το κρεβάτι

Many Greek neuter nouns end in -ο, -ι, or -μα, though not all nouns work exactly the same way.

Because both nouns are neuter singular, they both take το here.

A rough pronunciation guide:

• Το = toh
• τηλέφωνό = tee-LE-fo-NO
• μου = moo
• είναι = EE-ne
• κάτω = KA-toh
• από = a-PO
• το = toh
• κρεβάτι = kre-VA-ti

The main stresses are on:

• τηλέ
• φωνό
• εί
• κά
• πό
• βά

So the sentence sounds roughly like:

to tee-LE-fo-NO moo EE-ne KA-to a-PO to kre-VA-ti

In this sentence, είναι is the normal and correct choice.

• Το τηλέφωνό μου είναι κάτω από το κρεβάτι.
• My phone is under the bed.

Greek can sometimes omit είναι in very informal speech, headlines, notes, or certain fixed expressions, but for normal full sentences like this, you should keep it.

So as a learner, it is safest to use είναι.

Yes, Greek word order is more flexible than English, although the original sentence is the most neutral:

• Το τηλέφωνό μου είναι κάτω από το κρεβάτι.

You may also hear:

• Κάτω από το κρεβάτι είναι το τηλέφωνό μου.
• Το τηλέφωνό μου κάτω από το κρεβάτι είναι.
  This one is much less neutral and sounds marked or poetic.

The usual everyday order is:

subject + verb + location

So your sentence is the best standard version.

Yes. In everyday speech, από is often shortened before το, την, etc.

So:

• κάτω από το κρεβάτι

often becomes:

• κάτω απ’ το κρεβάτι

This is very common in spoken Greek and in informal writing. Both versions mean the same thing.

Both are possible, but they are not exactly the same.

• τηλέφωνο = phone / telephone
• κινητό = mobile phone / cell phone

If you mean specifically a mobile phone, many speakers would naturally say:

• Το κινητό μου είναι κάτω από το κρεβάτι.

If the context is general, το τηλέφωνό μου is still perfectly correct.

It breaks down like this:

• Το τηλέφωνό μου = my phone

  • το = the
  • τηλέφωνό = phone
  • μου = my

• είναι = is

• κάτω από το κρεβάτι = under the bed

  • κάτω από = under
  • το κρεβάτι = the bed

So the structure is:

subject + verb + prepositional phrase

That makes it a very useful model sentence for building your own Greek:

• Το βιβλίο μου είναι πάνω στο τραπέζι. = My book is on the table.
• Η τσάντα μου είναι κάτω από την καρέκλα. = My bag is under the chair.

Yes — Greek stress is very important and is always written.

Notice these stressed syllables:

• τηλέφωνο
• τηλέφωνό μου
• είναι
• κάτω
• από
• κρεβάτι

If you put the stress in the wrong place, your Greek may sound unnatural or even become hard to understand.

A particularly important point in this sentence is:

• τηλέφωνο
• τηλέφωνό μου

When μου is added after the noun, the written accent changes to reflect the correct spoken stress pattern. That is something worth getting used to early.