Learn Hardcore Swedish: Hon svarar genast när chefen ringer. - She answers immediately when the boss calls.

Hon — subject pronoun (she).
svarar — present tense of svara (to answer), a regular group 1 verb: svara–svarar–svarade–svarat.
genast — adverb (immediately).
när — subjunction (when).
chefen — definite singular of chef (boss/manager): en chef, chefen, chefer, cheferna.
ringer — present tense of ringa (to call), regular group 2: ringa–ringer–ringde–ringt.

Why is the present tense used (both svarar and ringer) even though this can refer to the future or a habit?

Swedish present covers current time, near future, and habitual actions. Hon svarar genast när chefen ringer can mean “She answers right away whenever the boss calls” (habit) or “She will answer right away when the boss calls” (future).

What word order rules are at play in the main clause and in the när-clause?

Main clause uses V2: subject + finite verb in second position. Hence: Hon svarar genast …
Subordinate när-clause: conjunction + subject + (sentence adverbs) + finite verb. Hence: när chefen ringer (not inverted).
If you front the när-clause: När chefen ringer, svarar hon genast. (comma after the fronted clause).

Do I need a comma before när here?

No. In modern Swedish you normally do not put a comma before a short subordinate clause that follows the main clause: Hon svarar genast när chefen ringer. If the när-clause comes first, add a comma after it: När chefen ringer, svarar hon genast.

Where does negation (inte) go?

In the main clause, inte comes after the finite verb: Hon svarar inte genast när chefen ringer.
In a subordinate när-clause, inte precedes the finite verb: när chefen inte ringer (grammatically correct, even if odd in meaning here).
Avoid när chefen ringer inte and Hon inte svarar … — both are ungrammatical.

Can I say när ringer chefen inside the sentence?

No. När ringer chefen? is a direct question (inversion). Inside a subordinate clause you keep normal order: när chefen ringer.

What’s the nuance of genast? Are there synonyms?

Genast means “immediately/right away.” Common near-synonyms:

Very common: direkt, på en gång, med detsamma
More formal: omedelbart
Potentially “soon/shortly” rather than strictly immediate: strax (context-dependent) All work in this sentence, with slight style differences: Hon svarar direkt …, … omedelbart …, etc.

Is svara transitive? Do I need på?

svara (någon) = answer someone: Hon svarar chefen genast.
svara på (något) = answer something: Hon svarar på mejlet/frågan.
Without an object (as in the original), svara just means “respond/answer.”

How do I talk about phone calls with ringa?

ringa (någon) or ringa till (någon) = call someone (both are common).
ringa upp (någon) = place a call to someone (often “call back/phone”).
ringa tillbaka = call back (return the call). Here, chefen ringer just means “the boss calls.”

Does chefen automatically mean “her boss”? How would I make that explicit — can I use sin?

chefen literally means “the boss (the one we both know from context).” In workplace talk it often implies one’s own boss, but it’s not explicit.
To make it explicit, use hennes chef: Hon svarar genast när hennes chef ringer.
Do not use sin here: reflexive sin refers to the subject of its own clause. In … när sin chef ringer, sin would refer to the subject of the när-clause (i.e., the boss), yielding “when the boss’s (own) boss calls,” which isn’t what you want.

Can I move genast around?

Neutral: Hon svarar genast …
With emphasis, you can front it: Genast svarar hon när chefen ringer. (marked, more stylistic)
Avoid Hon genast svarar … in neutral speech — it sounds unnatural.

How would I express “as soon as” instead of “when”?

Use så fort or så snart:

Hon svarar så fort chefen ringer.
Så snart chefen ringer, svarar hon. These already imply immediacy, so you usually don’t add genast.

Any quick pronunciation tips?

hon: like “hoon” (oo as in “food,” a bit shorter).
svarar: stress on the first syllable: SVA-rar; the sv- cluster is like English “sv.”
genast: g before e sounds like a y: roughly “YEH-nast.”
när: ä like the vowel in “air,” shorter; rolled or tapped r.
chefen: ch is the Swedish “sj”-sound — a breathy “sh” further back in the mouth: “SHEH-fen.”
ringer: ng like in English “sing,” then “-er.”