صاحبي تزحلق بغرفة التبديل.

In everyday Levantine, صاحبي is a very common colloquial way to say my friend or my buddy. صديقي is correct, but it sounds more formal and closer to Standard Arabic.

Also, the ending -ي means my, so:

صاحب = friend / companion
صاحبي = my friend

Because the possessive ending -ي already makes the noun definite. In Arabic, you do not normally use الـ together with a possessive suffix.

So:

صاحبي = my friend
not الصاحبي

تزحلق means slipped, slid, or skidded. In this sentence, it usually means someone lost their footing on a slippery surface.

It does not always have to mean a full fall. It can simply mean he slipped.

It is the past tense, specifically third person masculine singular.

So تزحلق means he slipped.

If the subject were feminine, you would say تزحلقت = she slipped.

Because in spoken Levantine, subject + verb word order is very common and natural.

So:

صاحبي تزحلق = My friend slipped

You can also sometimes hear تزحلق صاحبي, but صاحبي تزحلق sounds very normal in everyday speech.

Here, بـ is a preposition meaning in, at, or inside.

So:

بغرفة = in a room / in the room

In colloquial Arabic, prepositions often attach directly to the following word, so بـ + غرفة becomes بغرفة.

This is an iḍāfa construction, also called a noun-ownership or noun-linking structure.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

غرفة التبديل = the changing room

Literally, it is something like room of changing.

That is why you do not say الغرفة التبديل here.

Because the ة at the end of غرفة is pronounced when the word is linked to another word in an iḍāfa.

So on its own:

غرفة is often pronounced roughly ghurfeh

But in غرفة التبديل, it becomes more like:

ghurfet et-tabdīl or ghurfet it-tabdīl

So the ending sounds like -et when connected.

It comes from the root idea of changing, replacing, or switching.

So التبديل literally means something like changing or replacement. In this phrase, it refers to changing clothes, so غرفة التبديل means changing room.

Depending on context, English might also say dressing room or fitting room.

Yes, you can.

Both can mean in the changing room. In Levantine, بـ is very common in everyday speech and often sounds very natural in short sentences like this.

So both are possible:

صاحبي تزحلق بغرفة التبديل
صاحبي تزحلق في غرفة التبديل

The version with بـ is especially common colloquially.

A rough Levantine pronunciation is:

ṣāḥbi tzaḥlaʔ b-ghurfet it-tabdīl

A few notes:

• ص is a heavy s
• ح is a strong breathy throat sound
• ق at the end of تزحلق is often pronounced as a glottal stop ʔ in many Levantine accents, so تزحلق may sound like tzaḥlaʔ
• In التبديل, the ل of الـ is not clearly pronounced because ت is a sun letter, so it sounds more like et-tabdīl or it-tabdīl

You would usually change both the noun and the verb:

صاحبتي تزحلقت بغرفة التبديل

That means my female friend slipped in the changing room.

Changes:

• صاحبي → صاحبتي = my female friend
• تزحلق → تزحلقت = she slipped

Sometimes, yes. Depending on context, tone, and region, صاحبي can mean my friend, my buddy, or occasionally something closer to my guy / my companion. In some contexts, similar words can even overlap with boyfriend/girlfriend meanings, but that is highly context-dependent.

In this sentence, the most natural interpretation is simply my friend.