المصباح اليدوي بشنطة الظهر.

Because Arabic usually leaves out the present-tense verb to be.

So a sentence like المصباح اليدوي بشنطة الظهر naturally means The flashlight is in the backpack, even though there is no separate word for is.

This is very normal in both Standard Arabic and Levantine.
If you wanted past or future, then a verb would appear:

• كان المصباح اليدوي بشنطة الظهر = The flashlight was in the backpack
• رح يكون المصباح اليدوي بشنطة الظهر = The flashlight will be in the backpack

A word-for-word breakdown is:

• المصباح = the lamp
• اليدوي = hand-held / manual
• المصباح اليدوي = flashlight, literally the hand-held lamp
• بـ = in / at / with, depending on context
• شنطة = bag
• الظهر = the back
• شنطة الظهر = backpack, literally bag of the back

So the whole sentence is literally something like:

The hand-held lamp is in the back-bag.

In Levantine, بـ is extremely common and flexible. It can mean things like:

• in
• at
• with
• sometimes other related ideas depending on the expression

Here, بشنطة الظهر means in the backpack.

So although a learner may expect في for in, Levantine often uses بـ very naturally for location.

Examples:

• أنا بالبيت = I’m at home / in the house
• المفاتيح بالشنطة = The keys are in the bag

So المصباح اليدوي بشنطة الظهر is normal Levantine-style phrasing.

Yes, you could.

Both can work, but they may feel slightly different depending on speaker and situation:

• بشنطة الظهر = very natural colloquial Levantine
• في شنطة الظهر = also clear and common
• جوا شنطة الظهر = more explicitly inside the backpack

So if you want to emphasize physical containment, جوا is especially clear:

• المصباح اليدوي جوا شنطة الظهر

But the original sentence with بـ is completely natural.

Because this is an idafa construction, often called a noun + noun possessive structure.

In شنطة الظهر:

• شنطة = bag
• الظهر = the back

Together, it means backpack or literally bag of the back.

In an idafa:

• the first noun usually does not take الـ
• the second noun can be definite
• the whole phrase becomes definite because of the second noun

So:

• شنطة ظهر = a backpack
• شنطة الظهر = the backpack

That is why you do not say الشنطة الظهر here.

Yes. This is a very important point.

When شنطة stands alone, the final ة is usually pronounced like -a:

• شنطة = shanṭa / shanṭe

But when it is followed by another noun in an idafa, that ة is pronounced as t.

So:

• شنطة by itself
• شنطة الظهر = shanṭet/shanṭit eḍ-ḍahr depending on dialect and pronunciation style

So the phrase is not pronounced like two completely separate words. The first word links to the second.

That is one reason learners often miss the structure at first.

Because the الـ in الظهر is affected by a sun letter.

The letter ظ is one of the letters that causes assimilation of the l sound in الـ. So instead of pronouncing the l, speakers double the first consonant of the noun.

In careful Arabic, الظهر is something like:

• aẓ-ẓahr

In many Levantine accents, ظ is often pronounced closer to an emphatic d, so you may hear something like:

• eḍ-ḍahr
• ed-dahr

So in connected speech, شنطة الظهر may sound like:

• shanṭet eḍ-ḍahr

Because اليدوي is an adjective describing المصباح, and adjectives in Arabic must agree with the noun in gender and definiteness.

Here:

• مصباح is masculine singular
• so the adjective must also be masculine singular: يدوي
• since المصباح is definite, the adjective must also be definite: اليدوي

So:

• مصباح يدوي = a flashlight
• المصباح اليدوي = the flashlight

If the noun were feminine, the adjective would be feminine too.

Because Arabic adjectives agree with the noun in definiteness as well as gender and number.

So:

• مصباح يدوي = a flashlight
• المصباح اليدوي = the flashlight

This is different from English, where adjectives do not change for definiteness.

In Arabic, if the noun is definite, the adjective usually must be definite too.

It is understandable, but it sounds somewhat formal or Standard-Arabic-like.

In everyday Levantine, many speakers might say things like:

• فلاش
• فلاش لايت
• كشاف or كشّاف in some areas
• sometimes just مصباح depending on context

So the sentence is understandable, but the vocabulary is a bit mixed:

• بشنطة feels colloquial/Levantine
• المصباح اليدوي feels more formal or standard

A very everyday Levantine version might sound more like:

• الفلاش لايت بشنطة الظهر or
• الكشّاف بشنطة الظهر

Yes. This is a normal Arabic nominal sentence:

• المصباح اليدوي = topic / subject
• بشنطة الظهر = location phrase

So the structure is basically:

[the flashlight] + [in the backpack]

This is a very common pattern in Arabic for sentences meaning X is in Y.

You could sometimes rearrange things for emphasis, but the given order is straightforward and natural for a learner to recognize.