Dejo el móvil sobre la mesilla antes de acostarme.

Dejo is the present simple, and here it usually expresses a habit or something the speaker regularly does: I leave my phone on the bedside table before going to bed.

In Spanish, the simple present is often used where English might also use the simple present for routines:

• Dejo el móvil... = I leave my phone...

Estoy dejando would sound more like something happening right now, in progress:

• Estoy dejando el móvil sobre la mesilla = I’m putting/leaving the phone on the bedside table right now

So in this sentence, dejo is the natural choice for a usual action.

Spanish often uses the definite article (el, la, los, las) with personal belongings when it is already clear whose thing it is, especially when the owner is obvious from the context.

So:

• Dejo el móvil... literally says I leave the phone...
• But it naturally means I leave my phone...

This is very common in Spanish:

• Me lavo las manos = I wash my hands
• Me duele la cabeza = My head hurts

You can say mi móvil if you want to emphasize ownership, but it is not necessary here.

In Spain, el móvil usually means mobile phone / cell phone.

This is the normal everyday word in Spain:

• ¿Dónde está mi móvil? = Where’s my phone?

In many parts of Latin America, people more often say:

• celular
• teléfono celular

So el móvil is a very Spain-Spanish choice.

Here, la mesilla means a small table, and in this context it usually means a bedside table / nightstand.

In Spain, people often say:

• mesilla de noche = bedside table / nightstand

Sometimes mesilla by itself is enough if the context is clearly the bedroom.

Also, -illa is a diminutive ending, so historically mesilla is like little table.

Yes. In this sentence, sobre means on / on top of.

So:

• sobre la mesilla = on the bedside table

Spanish has several ways to express this idea:

• sobre la mesilla
• encima de la mesilla

Both can work. Sobre is a bit more compact and straightforward here.

Be careful: sobre can also mean about in other contexts:

• un libro sobre historia = a book about history

So the meaning depends on context.

After antes de, Spanish normally uses an infinitive when the subject is the same as in the main clause.

Here the subject of both actions is I:

• Dejo... = I leave
• acostarme = to go to bed

So Spanish uses:

• antes de acostarme = before going to bed

Not:

• antes de me acuesto ❌

If the subject changes, then Spanish usually uses antes de que + subjunctive:

• Lo hago antes de que te acuestes = I do it before you go to bed

So:

• same subject → antes de + infinitive
• different subject → antes de que + subjunctive

Because acostarse is a reflexive verb.

The full infinitive is:

• acostarse = to go to bed

When the speaker is talking about themselves, the reflexive pronoun is me:

• acostarme = to go to bed / literally to put myself to bed

In Spanish, reflexive pronouns can attach to an infinitive:

• voy a acostarme
• antes de acostarme

That is completely normal.

The accent mark in acostarme is there to keep the correct stress when the pronoun is attached.

Base infinitive:

• acostar

Reflexive infinitive:

• acostarme

When Spanish adds pronouns to infinitives, gerunds, or affirmative commands, a written accent is sometimes needed so the word keeps its original pronunciation.

So the accent in acostarme helps preserve the normal stress pattern.

Usually yes, in this kind of sentence.

• acostarse = to go to bed
• sometimes more literally: to lie down or to get oneself into bed

In everyday use, especially with antes de acostarme, the natural translation is before going to bed.

Depending on context, related ideas could be:

• irse a la cama = to go to bed
• dormirse = to fall asleep

These are not always interchangeable:

• acostarse focuses on getting into bed
• dormirse focuses on actually falling asleep

Yes, you could.

• sobre la mesilla = on the bedside table
• encima de la mesilla = on top of the bedside table

Both are correct. The difference is mostly one of style and nuance:

• sobre is shorter and a little neater
• encima de can sound a bit more explicit about physical position

In this sentence, sobre la mesilla sounds very natural.

Yes, Spanish word order is flexible, although the original sentence is the most neutral.

Original:

• Dejo el móvil sobre la mesilla antes de acostarme.

You could also hear:

• Antes de acostarme, dejo el móvil sobre la mesilla.

This puts more emphasis on before going to bed.

Both are correct. Spanish often moves phrases around for emphasis or rhythm more easily than English does.