Learn Hardcore German: Die Angewohnheit, abends lange aufs Handy zu schauen, stört meine Erholung. - The habit of looking at my phone for a long time in the evening disturbs my recovery.

Grammatically, that infinitive group functions like an adjective that specifies which habit:
Die Angewohnheit, [nämlich die Angewohnheit] abends lange aufs Handy zu schauen, …

In modern German spelling, the comma before such zu‑infinitive groups is often optional but very common here, because it makes the sentence easier to read. Most careful writers would keep this comma in this example.

What is the function of abends, and how is it different from am Abend?

abends is an adverb of time meaning in the evenings / at night (habitually). It describes how often or when something usually happens.

abends = in the evening(s) as a general, repeated time:
Ich lese abends. – I read in the evenings (as a habit).
am Abend = on one specific evening or a specific occasion:
Am Abend war ich müde. – In the evening (that day) I was tired.

In the sentence, abends fits well because Die Angewohnheit already suggests a repeated, habitual action.

Why is it lange and not lang?

Both lange and lang can appear in similar contexts, but here lange is the natural adverb form meaning for a long time.

lange is the usual adverb when you talk about duration:
lange schlafen, lange warten, lange aufs Handy schauen
lang is more common as an adjective:
ein langer Tag, eine lange Serie

In colloquial speech, you might sometimes hear lang aufs Handy schauen, but lange is more standard and sounds better in careful German.

What does aufs Handy mean exactly, and why is it a contraction?

aufs is the contraction of auf das:

auf (preposition) + das Handy (neuter, accusative) → aufs Handy

The verb (auf etwas) schauen takes auf with the accusative when it means to look at something:

aufs Handy schauen = to look at the phone (to look at its screen)

So lange aufs Handy schauen literally means to look at the phone for a long time.

Other common contractions:

an das → ans (z.B. ans Handy gehen – to answer the phone)
in das → ins
bei dem → beim, etc.

What is the difference between aufs Handy and auf dem Handy?

They express different ideas:

aufs Handy schauen (auf + Akkusativ)
= to look at the phone (target of your gaze)
auf dem Handy (auf + Dativ)
= on the phone (location of something)

Examples:

Ich schaue abends lange aufs Handy.
I stare at my phone for a long time in the evenings.
Der Film ist auf dem Handy.
The movie is on the phone (stored there).

So in the original sentence, you are not talking about something being located on the phone; you’re describing the act of looking at the phone, so aufs Handy is correct.

Why do we use zu schauen here instead of a finite verb form?

The phrase abends lange aufs Handy zu schauen is a zu‑infinitive clause. It acts like a noun phrase that explains what the habit is.

Structure:

Die Angewohnheit, [was denn?] abends lange aufs Handy zu schauen, …

In English we do something similar:

The habit of looking at my phone for a long time in the evening disturbs my rest.

German often uses zu + infinitive after abstract nouns like:

die Angewohnheit, ... zu ... – the habit of ...
der Plan, ... zu ... – the plan to ...
die Entscheidung, ... zu ... – the decision to ...

So zu schauen is required here because it makes an infinitive clause that depends on the noun Angewohnheit.

Why is the word order abends lange aufs Handy zu schauen and not in some other order?

Several elements are combined before the verb:

abends – time (when?)
lange – duration/manner (how long?)
aufs Handy – object / direction (at what?)
zu schauen – verb at the end of the infinitive clause

German often follows a time–manner–place (or goal) tendency, and in infinitive clauses the infinitive with zu normally comes at the end.

Other orders like lange abends aufs Handy zu schauen are possible but sound less natural.
abends lange aufs Handy zu schauen is the smooth, idiomatic order.

What does stört mean here, and what is its grammatical role?

stört is the 3rd person singular present form of the verb stören.

Infinitive: stören – to disturb, to bother, to interfere with
3rd person singular: er/sie/es stört

In the sentence:

Subject: Die Angewohnheit, abends lange aufs Handy zu schauen
Verb: stört
Object: meine Erholung

So literally:
The habit of looking at my phone for a long time in the evenings disturbs my recovery.

What exactly does meine Erholung mean, and why not mein Schlaf?

Erholung means rest, recovery, recuperation in a general sense. It includes:

physical rest
mental relaxation
recovery from stress

Schlaf is more specific: sleep.

So:

meine Erholung = my rest / my recovery (broader concept)
mein Schlaf = my sleep (specifically the sleeping part)

The sentence suggests that this habit harms not only sleep itself but the whole process of resting and recharging, so meine Erholung is a natural choice.

What are the genders and cases of Angewohnheit and Erholung in this sentence?

Both nouns are grammatically feminine:

die Angewohnheit (feminine)
die Erholung (feminine)

In this sentence:

Die Angewohnheit → nominative singular, subject of the sentence.
meine Erholung → accusative singular, direct object of stört.

Because feminine nouns have the same form for nominative and accusative in the singular (die), you see:

die Angewohnheit (Nom.)
die Erholung (Acc.)

The possessive meine also looks the same in nominative and accusative feminine singular:

meine Erholung (Acc.)
(it would also be meine Erholung in nominative)

Could this sentence be rephrased in another common way?

Yes. A very natural alternative is:

Es stört meine Erholung, wenn ich abends lange aufs Handy schaue.

Here:

Es is a dummy subject.
The clause wenn ich abends lange aufs Handy schaue explains the condition.
The core meaning is the same: this behavior disturbs your rest.

Another variation, a bit more colloquial, is:

Dass ich abends lange aufs Handy schaue, stört meine Erholung.

Is Handy a false friend for English speakers?

Yes. Handy in German does not mean useful or convenient like in English.

das Handy in German = mobile phone / cell phone / smartphone

So in the sentence, Handy refers to your mobile phone, usually your smartphone, not to something “handy” in the English sense.