افتكر تحط التليفون على الشاحن قبل ما تنام.

Yes. Here افتكر is an imperative, so it means remember.

The verb يفتكر in Egyptian Arabic can mean both remember and think, depending on context. In this sentence, since it comes first and is followed by an action someone should do, the natural meaning is remember to...

Context is what tells you it is an imperative here, not a past tense.

Because Egyptian Arabic does not use an infinitive like English to put.

In English, you say remember to put.
In Egyptian Arabic, after a verb like افتكر, the next verb is often put in the imperfect form:

• افتكر تحط = literally something like remember you-put
• natural English meaning: remember to put

So تحط is doing the job that to put does in English.

تحط is the imperfect form of حط, which means put / place.

Here it is the 2nd person singular masculine form, so literally it means you put.

That may feel strange to an English speaker, but after verbs like افتكر, عايز, لازم, and similar expressions, Egyptian Arabic often uses this kind of form where English would use an infinitive.

Because Egyptian Arabic often uses the definite article when the thing is already clear from context.

So التليفون here can naturally mean the phone, but in context it may effectively mean your phone if that is obvious.

Both are possible:

• التليفون = the phone
• تليفونك = your phone

Using تليفونك would be more explicit. Using التليفون sounds very natural if both people already know which phone is meant.

Literally, على الشاحن means on the charger.

That is a normal way to express this idea in Egyptian Arabic: putting a phone onto the charger / connecting it to charge.

• على = on
• الشاحن = the charger

So even though English may also say plug it in or put it on charge, Egyptian Arabic often uses this very physical image: put the phone on the charger.

قبل ما means before followed by a verb.

So:

• قبل ما تنام = before you sleep / before you go to sleep

This is a very common Egyptian structure:

• قبل ما + verb

It is one of the most natural colloquial ways to say before doing something.

No. Here ما is not negative.

In this expression, ما is just part of the structure قبل ما + verb. So:

• قبل ما تنام does not mean before you do not sleep
• it simply means before you sleep

This is a common thing learners ask about, because ما often does mark negation elsewhere, but not in this pattern.

تنام is the 2nd person singular masculine imperfect form: you sleep.

So this sentence is addressed to one male.

If you were speaking to a woman, you would usually say:

• افتكري تحطي التليفون على الشاحن قبل ما تنامي

If you were speaking to more than one person:

• افتكروا تحطوا التليفون على الشاحن قبل ما تناموا

This kind of agreement affects several words in the sentence, not just one.

It is clearly Egyptian colloquial Arabic.

Signs of that include:

• افتكر used this way in everyday speech
• تحط after another verb
• قبل ما تنام instead of a more formal structure

A more MSA-style version might be:

• تذكّر أن تضع الهاتف على الشاحن قبل أن تنام

That sounds much more formal and bookish.
The original sentence is what you are much more likely to hear in everyday Egyptian speech.

A rough pronunciation is:

efteker teḥoṭṭ et-telefōn ʿala sh-shāḥen abl ma tinām

A few notes:

• ḥ in teḥoṭṭ and shāḥen is a strong h sound from the throat
• ṭ in ḥoṭṭ is an emphatic t
• ʿ in ʿala is the Arabic letter ع
• sh-shāḥen has a doubled sh sound because the ال assimilates to ش

If you want a very rough English-style guide, you can think of it like:

ef-TE-ker te-HOTT et-tele-FOHN A-la sh-SHAA-hen abl ma te-NAAM

That is only approximate, but it is a useful starting point.