العاكس الضوئي على هيكل الدراجة.

Not really in the usual sense. It is most naturally a noun phrase or caption-like phrase, meaning something like the light reflector on the bicycle frame.

There is no verb here. In real-world Arabic, phrases like this are very common in:

• labels
• picture descriptions
• textbook captions
• interface text

If you wanted a full sentence, you could say something like:

• العاكس الضوئي على هيكل الدراجة موجود.
  The light reflector is on the bicycle frame.

But in many contexts, Arabic simply uses the shorter phrase.

Because in Arabic, adjectives normally come after the noun they describe.

So:

• العاكس = the reflector
• الضوئي = light / optical

Together:

• العاكس الضوئي = the light reflector

This is the normal Arabic order:

• noun + adjective

whereas English often uses:

• adjective + noun

Because the adjective must agree with the noun in definiteness.

Here, العاكس is definite because it has الـ:

• العاكس = the reflector

So the adjective must also be definite:

• الضوئي = the light/optical

That is why Arabic says:

• العاكس الضوئي

not:

• العاكس ضوئي

The adjective also agrees in:

• gender
• number
• case

Because هيكل الدراجة is an iḍāfa construction, often called a possessive construction.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun determines whether the whole phrase is definite

So:

• هيكل = frame
• الدراجة = the bicycle

Together:

• هيكل الدراجة = the frame of the bicycle / the bicycle’s frame

Since الدراجة is definite, the whole phrase becomes definite.

That is why Arabic says:

• هيكل الدراجة

not normally:

• الهيكل الدراجة

على means on or on top of / on the surface of.

So:

• على هيكل الدراجة = on the bicycle frame

This preposition is used because the reflector is understood to be attached on the frame.

Compare:

• على = on
• في = in
• تحت = under
• فوق = above

So على is the natural choice for something mounted on a bicycle frame.

عاكس literally comes from a root connected with reflecting or reversing. In this context, it means reflector.

So:

• عاكس = reflector
• العاكس الضوئي = light reflector

This is a good example of Arabic using a word that is originally an active-participle-type form as an ordinary noun.

Because ض is a sun letter. With sun letters, the l in الـ is not pronounced separately; instead, the next consonant is doubled.

So:

• الضوئي is pronounced roughly aḍ-ḍaw’ī

not:

• al-ḍaw’ī

By contrast, in العاكس, the ع is a moon letter, so the l is pronounced:

• al-ʿākis

And in الدراجة, د is also a sun letter, so it is pronounced roughly:

• ad-darrāja

A useful rough pronunciation is:

al-ʿākis aḍ-ḍaw’ī ʿalā haykal id-darrāja

A few notes:

• العاكس = al-ʿākis
• الضوئي = aḍ-ḍaw’ī
• على = ʿalā
• هيكل = haykal
• الدراجة = ad-darrāja in connected pronunciation

Two sounds may feel unfamiliar to English speakers:

• ع in العاكس and على: a deep throat sound
• ض in الضوئي: an emphatic d-like sound

A possible full vocalization is:

الْعَاكِسُ الضَّوْئِيُّ عَلَى هَيْكَلِ الدَّرَّاجَةِ

If you are wondering about the endings:

• العاكسُ and الضوئيُّ are nominative here if the phrase is treated as a standalone heading or noun phrase
• after the preposition على, هيكلِ is genitive
• in the iḍāfa, الدراجةِ is also genitive

In everyday reading and speech, especially in captions or simple text, those final case vowels are often not pronounced.

Yes. هيكل has a broader meaning than just frame in some contexts. It can mean:

• structure
• framework
• skeleton
• chassis/body structure

In this sentence, though, هيكل الدراجة most naturally means the bicycle frame or the body/frame structure of the bicycle.

So the exact English wording can vary a little depending on context, but bicycle frame is usually the best simple translation.