Learn Hardcore Russian: Я часто читаю электронные книги на телефоне вечером. - I often read e‑books on my phone in the evening.

Breakdown of Я часто читаю электронные книги на телефоне вечером.

Why is it читаю and not читать in this sentence?

Читать is the infinitive form: to read.
Читаю is the 1st person singular present tense form: I read / I am reading.

Russian needs a conjugated verb in a normal sentence with a subject:

So with я you must use читаю, not the infinitive читать.

Does я часто читаю mean “I often read” or “I am often reading”? How do Russians express this?

Russian present tense usually covers both English simple present and present continuous:

Я часто читаю электронные книги…
= I often read e‑books…
also naturally understood as I often spend time reading e‑books…

If you need to emphasize “right now”, you can add words like:

But without extra words, читаю itself works for both “read” and “am reading”; часто adds the idea of a regular habit.

What is часто exactly, and where can it go in the sentence?