Não mexas no meu telemóvel enquanto eu estou a estudar.

Because in European Portuguese, the negative imperative for tu uses the present subjunctive.

• Affirmative: Mexe! = Touch it / Move it / Stop fiddling? depending on context
• Negative: Não mexas! = Don’t touch it / Don’t mess with it

So não mexas is the correct tu form here.

Here, mexer means something like to touch, to mess with, to fiddle with, or to tamper with.

It is a very flexible verb:

• mexer = to move, stir, shake
• mexer em alguma coisa = to touch or mess with something

So não mexas no meu telemóvel is not just don’t move my phone. It more naturally means don’t touch / don’t mess with my phone.

Because mexer often takes the preposition em when it means to mess with / touch something.

So the structure is:

• mexer em o meu telemóvel

But em + o contracts to no:

• em + o = no

That gives:

• mexer no meu telemóvel

This kind of contraction is very common in Portuguese.

In European Portuguese, it is very common to use the definite article before possessives:

• o meu telemóvel
• a minha casa
• os meus amigos

For an English speaker, this can feel unusual, because English normally says just my phone, not the my phone. But in Portuguese, o meu telemóvel is the normal pattern.

In this sentence, because of the contraction with em, you see no meu telemóvel instead of em o meu telemóvel.

Because this is European Portuguese.

In Portugal, the usual word is:

• telemóvel = mobile phone / cell phone

In Brazil, the usual word is:

• celular

So if you are learning Portuguese from Portugal, telemóvel is the natural choice.

Because European Portuguese normally expresses the progressive with:

• estar a + infinitive

So:

• estou a estudar = I am studying

In Brazilian Portuguese, the more common form is:

• estou estudando

Both may be understood, but estou a estudar is the normal European Portuguese form.

The a is part of the European Portuguese progressive construction:

• estar a + infinitive

Examples:

• Estou a comer = I am eating
• Está a chover = It is raining
• Estamos a trabalhar = We are working

So in estou a estudar, the a does not mean to in the English sense. It is just part of the verbal structure that means be doing something.

No, it is not necessary.

Portuguese often leaves out subject pronouns because the verb ending already shows the person:

• enquanto estou a estudar

is perfectly natural.

Adding eu can give:

• extra emphasis
• contrast
• clarity

So enquanto eu estou a estudar is not wrong at all, but eu is optional here.

Enquanto means while.

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

• Não mexas no meu telemóvel enquanto eu estou a estudar.
• Don’t mess with my phone while I’m studying.

It is the natural word here because the sentence is about simultaneous actions.

Because the speaker is talking about a real, ongoing situation: I am studying.

So the indicative is used:

• enquanto eu estou a estudar

If the clause referred to something more hypothetical or dependent on another context, a different structure might appear. But here the speaker is simply describing what is happening, so estou is the normal choice.

It is informal, because mexas is the tu form.

So this is how you would speak to:

• a friend
• a sibling
• a child
• someone you address as tu

A more formal version would use você or another formal form, for example:

• Não mexa no meu telemóvel enquanto estou a estudar.

And for more than one person:

• Não mexam no meu telemóvel enquanto estou a estudar.

Yes, you could, but the nuance is slightly different.

• tocar = to touch
• mexer em = to touch, handle, fiddle with, mess with

So:

• Não toques no meu telemóvel = Don’t touch my phone
• Não mexas no meu telemóvel = Don’t mess with / don’t handle / don’t fiddle with my phone

In many situations both are possible, but mexer em often suggests a bit more than simple physical contact.

They help with pronunciation.

• não has ã, which shows a nasal sound
• telemóvel has an acute accent on ó, which shows the stressed syllable and the quality of the vowel

So:

• não is nasal
• telemóvel is stressed on mó

The accent in telemóvel also helps distinguish the natural pronunciation pattern.