Learn Hardcore Indonesian: Pengemudi ojek menghubungi saya; telepon saya berdering keras. - The motorcycle taxi driver contacts me; my phone rings loudly.

Menghubungi means “to contact” in a general sense (could be by call, text, chat).
Menelepon/menelpon means “to call (by phone)” specifically.
Because the second clause says the phone rang, you could also say Pengemudi ojek menelepon saya, which is a bit more specific. The original with menghubungi is still fine and natural.

Is the semicolon natural in Indonesian?

Semicolons exist in Indonesian, but they’re used less often than in English. Most writers would use:

A comma + conjunction: Pengemudi ojek menghubungi saya, jadi/sehingga/kemudian telepon saya berdering keras.
Or a period: Pengemudi ojek menghubungi saya. Telepon saya berdering keras. The semicolon isn’t wrong, just rarer and a bit formal.

Is telepon saya the most natural way to say “my phone” today?

Everyday speech usually says HP saya (handphone). More formal writing prefers ponsel saya. Telepon saya is correct but may sound like a landline to some.

Natural: HP saya berdering keras.
Formal: Ponsel saya berdering keras.

What’s the difference between berdering and berbunyi?

Berdering = “to ring” (a phone/bell).
Berbunyi = “to make a sound” (general). Both work for a phone, but berdering is the precise verb for ringing.

Is berdering keras the best way to say “rang loudly”? What about dengan keras, kencang, or nyaring?

Berdering keras is natural and common.
Berdering dengan keras is also fine; slightly more formal/emphatic.
Berdering kencang is very common in casual speech.
Berdering nyaring suggests a sharp, piercing ring. You can intensify with sekali or sangat: berdering keras sekali / sangat keras.

Can I put the adverb before the verb, like “keras berdering”?

No. In Indonesian, degree words/adjectives that function adverbially usually come after the verb:

Correct: berdering keras, berdering sangat keras
Not natural: keras berdering

Why is it menghubungi saya (direct object) and not menghubungi kepada saya?

Because menghubungi is a transitive verb that takes a direct object. You don’t use kepada with it. Say menghubungi saya, not menghubungi kepada saya.

How do I show past time? Indonesian has no tense marking here.

Add a time word:

Just now: Barusan/tadi pengemudi ojek menghubungi saya.
Yesterday: Kemarin pengemudi ojek menghubungi saya.
A moment ago: Baru saja pengemudi ojek menghubungi saya.

Could I make it passive: “I was contacted by the ojek driver”?

Yes:

Saya dihubungi pengemudi ojek; telepon saya berdering keras.
You can add oleh (by) for clarity/formality: Saya dihubungi oleh pengemudi ojek.

Why use saya and not aku? And what about -ku?

Saya is neutral/formal; works in most contexts.
Aku is informal/intimate.
Possessive clitic -ku is informal and attaches to nouns: teleponku/HP-ku. Examples:
Formal/neutral: Pengemudi ojek menghubungi saya; telepon saya berdering keras.
Casual: Pengemudi ojek menghubungi aku; HP-ku berdering keras.

Do I need to repeat saya in telepon saya? Can I drop it?

If context is clear, you can drop it:

Telepon berdering keras. (A phone—assumed to be yours from context.) You can also use -nya for “the/that/his/her/its” (context-dependent):
Teleponnya berdering keras. (the/that/his/her phone)

Should it be menelepon or menelpon? And what about telepon vs telpon?

Standard spellings (per KBBI):

telepon (noun)
menelepon (verb) Common informal variants:
telpon, menelpon, nelfon/nelfon (very common in speech/texting but nonstandard in formal writing)

Is pengemudi ojek the most natural term? What about tukang ojek, sopir, or driver?

Pengemudi ojek: neutral/formal; perfectly correct.
Tukang ojek: common and colloquial/traditional.
Driver ojek/driver ojol: colloquial, influenced by English; ojol = ojek online (ride-hailing).
Sopir usually refers to car drivers, not motorcycle taxis.

Can I force the meaning “a(n) ojek driver” vs “the ojek driver”?

Indonesian doesn’t mark definiteness by articles. Use:

Seorang pengemudi ojek = “an ojek driver.”
Context typically supplies “the.” You can also use si for a specific known person in informal contexts: Si pengemudi ojek itu…

Could I connect the clauses with yang?

Not as is. Yang starts a relative clause and needs a main clause after it. Incorrect:

✗ Pengemudi ojek yang menghubungi saya; telepon saya berdering keras. Correct options:
Pengemudi ojek yang menghubungi saya membuat telepon saya berdering keras.
Or keep two clauses with a conjunction/period.

What’s the morphology/nuance of menghubungi vs menghubungkan?

Menghubungi = meN- + hubung + -i → “to contact (someone).”
Menghubungkan = meN- + hubung + -kan → “to connect/link (something) to (something).” Examples:
Saya akan menghubungi Anda besok. (I’ll contact you tomorrow.)
Tolong hubungkan saya dengan bagian keuangan. (Please connect me to the finance department.)