Learn Hardcore Dutch: Tom controleert de instelling op zijn telefoon.

controleren = to check, to inspect, to verify
English to control (in the sense of "to manage, to be in charge of") is usually beheersen, regelen, or besturen in Dutch, depending on context.

So:
Tom controleert de instelling op zijn telefoon.
= Tom checks the setting on his phone.

What is the infinitive of controleert, and how is it conjugated?

The infinitive is controleren (to check).

Present tense (regular -eren verb):

ik controleer – I check
jij / je controleert – you check
hij / zij / het controleert – he / she / it checks
wij controleren – we check
jullie controleren – you (plural) check
zij controleren – they check

So with Tom (3rd person singular), you use controleert:
Tom controleert …

Why is it de instelling and not het instelling?

Because instelling is a de-word (common gender) in Dutch:

de instelling – the setting / the institution
een instelling – a setting / an institution

There is no rule that all words ending in -ing are de-words, but very many of them are (e.g. de rekening, de opening, de opleiding, de vergadering). Instelling fits this pattern and is also de.

Could instelling also mean something else, like institution?

Yes. Instelling has at least two common meanings:

setting (on a device, program, etc.)
- de instelling van je telefoon – the setting of your phone
institution / organization
- een medische instelling – a medical institution
- een onderwijsinstelling – an educational institution

In your sentence, because of op zijn telefoon, it clearly means a (phone) setting, not an institution.

Why is it de instelling (with the) and not een instelling (a setting)?

Dutch uses the definite article de here because we are usually talking about a specific setting, one that is known from context:

Maybe Tom has just been told: "Change the brightness setting."
Then: Tom controleert de instelling op zijn telefoon.

If you said een instelling, it would have a more vague meaning:

Tom controleert een instelling op zijn telefoon.
→ Tom checks a (certain) setting on his phone. (we don’t know which one)

Both are grammatically correct; the choice depends on whether the setting is specific/known (de) or not (een).

Why is the preposition op used: op zijn telefoon and not aan or in?

In Dutch, op is commonly used for things you do with or on a device/interface:

op zijn telefoon – on his phone
op de computer – on the computer
op mijn tablet – on my tablet

Rough differences:

op zijn telefoon
→ using / within the phone as a device or interface
aan de telefoon
→ on the phone talking to someone (on a call)
- Ik ben aan de telefoon. – I’m on the phone (in a call).
in zijn telefoon is unusual in this context; you’d normally not say that for software/settings.

So:
Tom controleert de instelling op zijn telefoon.
= He is checking the setting using his phone’s interface.

Could I move op zijn telefoon somewhere else in the sentence?

Yes, Dutch word order here is flexible. All of these are grammatically correct:

Tom controleert de instelling op zijn telefoon. (most natural)
Tom controleert op zijn telefoon de instelling. (also fine, a bit more marked)
Op zijn telefoon controleert Tom de instelling. (fronted for emphasis on on his phone)

Neutral, everyday speech would usually keep the original order:
Tom controleert de instelling op zijn telefoon.

How would this sentence look in a subordinate clause?

In a subordinate clause, the finite verb goes to the end:

Main clause:

Tom controleert de instelling op zijn telefoon.

Subordinate clause (after dat = that):

… dat Tom de instelling op zijn telefoon controleert.
→ … that Tom checks the setting on his phone.

So the core change is: controleert moves to the end of the clause.

Why is it zijn telefoon? Could it also be haar telefoon?

Zijn is the possessive for a male person (his) or for a neuter noun (its).
Haar is the possessive for a female person (her).

Here, the owner of the phone is Tom, who is male, so zijn telefoon = his phone.

Tom controleert de instelling op zijn telefoon.
→ Tom checks the setting on his phone.
Lisa controleert de instelling op haar telefoon.
→ Lisa checks the setting on her phone.

Note: zijn can also be used generically as “one’s” in some expressions, but here it’s simply Tom’s phone.

What are the genders of telefoon and instelling?

Both are de-words (common gender):

de telefoon – the phone
- een telefoon – a phone
- zijn telefoon / haar telefoon – his / her phone
de instelling – the setting / the institution
- een instelling – a setting / an institution

You will say die telefoon and die instelling for “that phone / that setting”.

Can I use the plural instellingen here? What would change?

Yes, grammatically you can:

Tom controleert de instellingen op zijn telefoon.
→ Tom checks the settings on his phone.

Difference:

de instelling (singular): one specific setting
de instellingen (plural): several settings, or the settings menu as a whole

So you choose singular or plural based on what you want to say.

Is controleren a separable verb? Why doesn’t anything split off?

Controleren is not a separable verb. It stays in one piece:

ik wil de instelling controleren – I want to check the setting
Tom controleert de instelling – Tom checks the setting

A separable verb would look like aanzetten (to switch on):

Tom zet zijn telefoon aan. – The verb splits: zet … aan in the main clause.
Infinitive: aanzetten

Controleren behaves like a normal non‑separable verb, so you never split it.

Can I say Tom checkt de instelling op zijn telefoon using checken?

Yes, that is possible in informal Dutch:

Tom checkt de instelling op zijn telefoon.

Checken is an English loan verb used in casual speech, especially among younger speakers or in tech contexts. Nuance:

controleren – more neutral/standard, fine in written and formal language
checken – more informal/colloquial, often in spoken language

For learners, it’s safe to prefer controleren; you will still understand checken when you hear it.