استلفت قلم من زميلي بالمكتب.

استلفت means I borrowed.

• استلف = to borrow
• استلفت = I borrowed

A very useful contrast in Levantine is:

• استلفت منك قلم = I borrowed a pen from you
• سلّفتك قلم = I lent you a pen

So the sentence is using the borrow verb, not the lend verb.

Because the ending -ت on استلفت already tells you the subject is I in the past tense.

So:

• استلفت = I borrowed

You can add أنا if you want emphasis:

• أنا استلفت قلم من زميلي بالمكتب

But in normal speech, Arabic often leaves the subject pronoun out because the verb already shows it.

Arabic does not have a separate indefinite article like English a / an.

So:

• قلم = a pen
• القلم = the pen

In dialect, this is completely normal. Also, colloquial Levantine drops the case endings you would see in formal Arabic, so you get قلم instead of formal قلماً.

من means from.

زميل means colleague / classmate / fellow student / peer, depending on context.

The ending -ي means my.

So:

• زميلي = my colleague / my classmate
• من زميلي = from my colleague

If the colleague is female, you would usually say:

• من زميلتي = from my female colleague

Not by itself. زميل is a general word for someone you study or work with.

Depending on context, it can mean:

• classmate
• coworker
• fellow student
• colleague

In this sentence, because of بالمكتب, the natural reading is coworker / office colleague.

In Levantine, the prefix بـ very often means in / at with places.

So:

• بالمكتب = in the office / at the office

This is very common in spoken Levantine.
You can also say في المكتب, and that may sound a bit more explicit or a bit closer to formal Arabic, but بالمكتب is very natural colloquial speech.

Also notice that the preposition attaches to the noun:

• ب + المكتب = بالمكتب

It is usually pronounced something like bil-maktab.

مكتب can mean either office or desk, depending on context.

In this sentence, بالمكتب most naturally means at/in the office.

It can be understood in two closely related ways:

• as the location of the borrowing
• as identifying which colleague you mean: my colleague at the office

Usually context makes this clear, and in everyday speech speakers do not always separate those meanings very strictly.

A rough pronunciation would be:

istalaft ʔalam min zmīli bil-maktab

A few notes:

• قلم is often pronounced ʔalam in many urban Levantine accents, because ق becomes a glottal stop.
• In some regions, people may keep ق as q, so you may also hear something closer to qalam.
• زميلي often sounds like zmīli.
• بالمكتب is commonly bil-maktab.

Regional pronunciation varies across Syrian, Lebanese, Palestinian, and Jordanian speech.

No. Arabic word order is fairly flexible.

This sentence is natural as:

• استلفت قلم من زميلي بالمكتب

But you could also hear:

• أنا استلفت قلم من زميلي بالمكتب
• استلفت من زميلي قلم
• قلم استلفته من زميلي بالمكتب

The core meaning stays similar, but the emphasis can shift a little depending on what comes first.

It feels mainly colloquial/Levantine.

Why?

• there are no formal case endings
• بـ is being used for in / at
• استلف is very common in everyday speech

A more formal MSA-style version would more likely be:

استعرتُ قلمًا من زميلي في المكتب

That is the kind of version you would expect in formal writing or textbook-style Standard Arabic.