Αν το περβάζι είναι βρεγμένο, δεν αφήνω πάνω του ούτε το ξυράφι ούτε το κινητό μου.

Because βρεγμένο has to agree with το περβάζι.

• περβάζι is neuter singular
• so the adjective must also be neuter singular
• that gives βρεγμένο

So:

• ο ... βρεγμένος = masculine
• η ... βρεγμένη = feminine
• το ... βρεγμένο = neuter

Here, το περβάζι είναι βρεγμένο means the sill/ledge is wet.

Αν means if and introduces a condition.

In this sentence, Αν το περβάζι είναι βρεγμένο means If the sill is wet.

Greek often uses αν + present for a real or likely condition, especially in general statements. So this sentence sounds like a general rule or habit:

• If the sill is wet, I don’t leave...

It is not necessarily talking about just one future moment. It can mean whenever that happens, this is what I do.

Because the sentence is phrased as a general habit / usual reaction.

• είναι = is
• αφήνω = I leave / I put down / I let remain

So δεν αφήνω here is not just a simple present in the English sense. It can mean something like:

• I don’t leave
• I won’t leave
• I never leave

depending on context.

In other words, Greek present tense is very natural here for a general rule: If the sill is wet, I don’t leave either the razor or my phone on it.

If you wanted a more clearly one-time future meaning, Greek would often use θα:

• Αν το περβάζι είναι βρεγμένο, δεν θα αφήσω...

Yes, but that is normal in Greek.

Greek regularly uses negative concord, which means several negative elements can appear together in the same sentence without canceling each other.

So:

• δεν αφήνω = I don’t leave
• ούτε το ξυράφι ούτε το κινητό μου = neither the razor nor my phone

Together they mean: I don’t leave either the razor or my phone on it
or more literally: I leave on it neither the razor nor my phone

In English, we usually avoid that kind of combination, but in Greek it is standard.

ούτε ... ούτε means neither ... nor.

Here it links two noun phrases:

• ούτε το ξυράφι
• ούτε το κινητό μου

So the structure is:

• δεν + verb + ούτε X ούτε Y

This is a very common Greek pattern for saying not X and not Y.

Examples:

• Δεν θέλω ούτε καφέ ούτε τσάι.
  I want neither coffee nor tea.
• Δεν είδα ούτε τον Γιάννη ούτε τη Μαρία.
  I saw neither Giannis nor Maria.

Because in Greek each noun phrase normally keeps its own article.

So Greek says:

• ούτε το ξυράφι ούτε το κινητό μου

not usually something like:

• ούτε ξυράφι ούτε κινητό μου in this context

The repeated article makes each item a complete noun phrase. This is very natural Greek, especially when you are talking about specific things:

• the razor
• my phone

πάνω του means on it or more literally on top of it.

It refers back to το περβάζι.

Why του?

Because Greek often uses a weak genitive pronoun after words like πάνω:

• πάνω μου = on me
• πάνω σου = on you
• πάνω του = on him / on it
• πάνω της = on her / on it
• πάνω μας = on us

A detail that often surprises learners: for a neuter singular noun like το περβάζι, the weak genitive pronoun is also του. So here του means of it / on it, referring to the neuter noun.

Yes, it could, but πάνω του is the more natural and compact choice here.

Compare:

• πάνω του = on it
• πάνω σε αυτό = on that / on it

πάνω σε αυτό is more explicit and can sound more emphatic or heavier. In everyday Greek, when the reference is clear, πάνω του is very common.

So in this sentence, πάνω του is the most natural way to say on it.

Because the normal Greek way to say my phone is:

• article + noun + possessive clitic
• το κινητό μου

This is the standard pattern:

• το βιβλίο μου = my book
• η τσάντα σου = your bag
• το σπίτι μας = our house

So μου comes after the noun.

You may sometimes see other orders for emphasis, but the neutral everyday form is το κινητό μου.

Here αφήνω means something like:

• leave
• set down
• leave lying
• leave resting

So δεν αφήνω πάνω του means: I don’t leave it on there / I don’t put it and leave it there.

It does not just mean leave in the sense of go away from. In Greek, αφήνω is often used for leaving an object somewhere:

• Άφησα τα κλειδιά στο τραπέζι.
  I left the keys on the table.

So in your sentence, it means not placing those objects on the wet sill.

Very often, yes: περβάζι commonly means windowsill.

But depending on context, it can also mean a ledge or sill more generally.

So if the wider context is a window, windowsill is the most likely meaning. If the context is more general, ledge/sill can also fit.

Yes. Greek word order is flexible.

For example, these are also possible:

• Αν το περβάζι είναι βρεγμένο, δεν αφήνω ούτε το ξυράφι ούτε το κινητό μου πάνω του.
• Δεν αφήνω πάνω του ούτε το ξυράφι ούτε το κινητό μου, αν το περβάζι είναι βρεγμένο.

The original order puts πάνω του before the ούτε ... ούτε phrase, which is perfectly natural. It highlights the location early:

• I don’t leave on it...

Greek often moves elements around for emphasis, rhythm, or focus, while keeping the meaning basically the same.