Έχω έννοια γιατί δεν απαντάει στο τηλέφωνο.

Yes. Έννοια has more than one meaning in Greek.

In expressions like έχω έννοια and μην έχεις έννοια, it means concern, worry, or something on your mind. So Έχω έννοια is an idiomatic way to say I’m worried or I’m concerned.

So this is one of those cases where the noun does not mean its more abstract dictionary sense of concept/notion.

Yes, it is natural and understandable.

It is a set expression meaning I’m concerned / I’m worried. A learner should just treat it as an idiomatic phrase rather than translating it word-for-word.

A very common alternative is Ανησυχώ γιατί δεν απαντάει στο τηλέφωνο, which also means I’m worried because he/she isn’t answering the phone.

Because Greek often leaves the subject pronoun out when it is already clear from the verb ending.

απαντάει is third person singular, so it can mean:

• he answers / is answering
• she answers / is answering
• sometimes it answers / is answering, depending on context

This is very normal in Greek. If you add αυτός or αυτή, it usually gives emphasis or contrast.

In Modern Greek, γιατί can mean both why and because.

You tell the difference from the structure and punctuation:

• Γιατί δεν απαντάει στο τηλέφωνο; = Why isn’t he/she answering the phone?
• Έχω έννοια γιατί δεν απαντάει στο τηλέφωνο. = I’m worried because he/she isn’t answering the phone.

So in your sentence, γιατί introduces the reason.

Δεν is the normal negative particle used with indicative verbs in Greek.

So:

• απαντάει = he/she answers / is answering
• δεν απαντάει = he/she does not answer / is not answering

Putting δεν directly before the verb is the standard pattern.

απαντάει is the present tense.

In Greek, the present tense often covers both ideas that English separates into:

• simple present: answers
• present continuous: is answering

So δεν απαντάει can mean either:

• doesn’t answer
• isn’t answering

In this sentence, the context makes isn’t answering the phone the most natural English translation.

Yes. Both απαντά and απαντάει are used in Modern Greek.

They are simply two present-tense forms of the same verb:

• απαντά
• απαντάει

In everyday speech, απαντάει is very common. απαντά is also correct and may sound a little shorter or slightly more formal depending on context and speaker.

Because Greek uses the verb απαντάω / απαντώ with σε in this expression.

στο is just the contracted form of:

• σε + το = στο

So:

• στο τηλέφωνο literally looks like to/on the phone
• but the whole phrase απαντάει στο τηλέφωνο means answers the phone

This is simply the Greek construction. It is more helpful to learn the whole phrase together than to translate each word separately.

Greek uses the definite article very often, including in many expressions where English uses it differently.

Here το is completely normal:

• στο τηλέφωνο = on/to the phone as part of the idiom

So the presence of το is not special or emphatic. It is just how the phrase is normally formed in Greek.

Usually, no.

In a short sentence like Έχω έννοια γιατί δεν απαντάει στο τηλέφωνο, it is normal to write it without a comma.

Greek punctuation is not always identical to English punctuation, but here no comma is the most straightforward choice.