Peux-tu décrocher pendant que je termine ce message, puis raccrocher si c’est le mauvais numéro ?

Both mean Can you...?, but Peux-tu uses inversion, which is a standard way to ask a question in French.

• Peux-tu décrocher ? = Can you answer/pick up?
• Tu peux décrocher ? = also common, but a bit more conversational

So Peux-tu sounds natural and correct, especially in neutral written French.

Because the subject is tu.

The verb pouvoir in the present tense goes like this:

• je peux
• tu peux
• il/elle/on peut
• nous pouvons
• vous pouvez
• ils/elles peuvent

So:

• tu peux
• therefore, with inversion: Peux-tu ?

Here, décrocher means to pick up the phone / answer the phone.

Its literal meaning is something like to unhook, which comes from older telephones where you physically lifted the receiver off the hook. That is why it became the normal verb for answering a call.

So in this sentence:

• décrocher = pick up / answer

They are very close, but not always identical.

• décrocher = pick up the phone
• répondre au téléphone = answer the phone

In many situations, they mean almost the same thing. But décrocher focuses more on the action of picking up, while répondre focuses more on answering.

Examples:

• Tu peux décrocher ? = Can you pick up?
• Tu peux répondre au téléphone ? = Can you answer the phone?

Both are natural here, but décrocher fits especially well because the sentence later uses raccrocher, which creates a nice pair:

• décrocher = pick up
• raccrocher = hang up

Because they depend on peux-tu.

After pouvoir (can / to be able to), French normally uses an infinitive:

• Peux-tu décrocher... ?
• literally: Can you pick up...?

The same pattern continues later in the sentence:

• puis raccrocher
• understood as and then [can you] hang up

So the infinitives are there because they are actions linked to can you.

Pendant que means while.

It introduces an action happening at the same time as another action:

• pendant que je termine ce message
• while I finish this message

It is followed here by the indicative: je termine. That is normal, because this is a real, factual action, not a hypothetical one.

French uses the indicative after pendant que:

• pendant que je mange = while I’m eating
• pendant qu’il travaille = while he’s working

Je termine is present tense and works naturally after pendant que to describe something currently in progress or happening right now.

• pendant que je termine ce message = while I finish/am finishing this message

You could think of it as very close to English while I finish or while I’m finishing.

Why not the others?

• je finirai = I will finish → future, not right for while
• je finis is also possible in some contexts, but terminer ce message sounds especially natural when talking about completing a message you are currently writing

In practice, terminer emphasizes bringing it to completion.

Here puis means then.

So:

• ..., puis raccrocher...
• ..., then hang up...

Yes, it is related to et puis, which can also mean and then. In this sentence, puis is slightly more concise and fits well in a written instruction.

Compare:

• Décroche, puis raccroche. = Pick up, then hang up.
• Décroche, et puis raccroche. = also possible, a bit heavier here

Raccrocher means to hang up.

Like décrocher, it comes from old telephone vocabulary:

• décrocher = take the receiver off the hook
• raccrocher = put it back on the hook

So they are a natural pair:

• décrocher = pick up
• raccrocher = hang up

That is why this sentence sounds very idiomatic.

French usually says c’est le mauvais numéro for it’s the wrong number.

Word-for-word:

• mauvais = bad / wrong
• numéro = number

So:

• le mauvais numéro = the wrong number

This is the normal French way to say it in this kind of situation.

You could also hear:

• Vous avez fait le mauvais numéro. = You dialed the wrong number.
• Ce n’est pas le bon numéro. = This isn’t the right number.

French usually uses c’est before a noun phrase like le mauvais numéro.

• c’est le mauvais numéro = it’s the wrong number

That is the standard structure.

Il est is generally used more with adjectives without an article:

• Il est occupé. = He is busy.
• but
• C’est un numéro occupé. / C’est le mauvais numéro.

So c’est is the correct choice here.

Yes, numéro is masculine:

• un numéro
• le numéro

Because it is masculine, the adjective must also be masculine:

• le mauvais numéro

If the noun were feminine, you would use mauvaise instead:

• la mauvaise adresse = the wrong address

But here it must be:

• le mauvais numéro

It is informal, because it uses tu.

• Peux-tu... ? = informal singular
• Pouvez-vous... ? = formal singular or plural

So this sentence sounds like you are speaking to:

• a friend
• a family member
• a coworker you know well
• a child

A formal version would be:

• Pouvez-vous décrocher pendant que je termine ce message, puis raccrocher si c’est le mauvais numéro ?

Yes, absolutely.

These are both correct:

• Peux-tu décrocher... ?
• Est-ce que tu peux décrocher... ?

The second is often easier for learners because it does not use inversion.

They mean the same thing, but the tone differs slightly:

• Peux-tu... ? = a bit more compact, standard
• Est-ce que tu peux... ? = very common in speech, often feels a little more relaxed

Because French can omit repeated words when the meaning is clear.

The full version would be something like:

• Peux-tu décrocher pendant que je termine ce message, puis peux-tu raccrocher si c’est le mauvais numéro ?

But that sounds repetitive. So French normally says:

• Peux-tu décrocher..., puis raccrocher... ?

The second infinitive raccrocher is still understood as depending on Peux-tu.

A very natural spoken version might be:

• Tu peux décrocher pendant que je finis ce message, puis raccrocher si c’est le mauvais numéro ?

Or even:

• Tu peux répondre pendant que je finis ce message, et raccrocher si c’est le mauvais numéro ?

The original sentence is already good French, but everyday speech often prefers:

• Tu peux... ? instead of Peux-tu... ?
• sometimes finis instead of termine
• sometimes répondre instead of décrocher

The original version sounds clear, correct, and natural, especially in neutral written French.