Learn Farsi: دانشجوها اغلب در کلاس گوشی چک می‌کنند. - The students often check their phones in class.

Adverbs of frequency like aghlab usually come right after the subject. In this sentence, it is placed directly after the subject daneshjoo-ha (the students) and before the location dar kelas (in class).

The translation says their phones, but is there a word for their here?

No, there is no word for their in this Farsi sentence. When it is completely obvious from the context who owns the object, Farsi speakers often drop the possessive ending. They just say gooshi (phone).

Why is the word gooshi singular if multiple students are checking their phones?

In English, we say they check their phones (plural) because there are multiple phones in total. In Farsi, if each person in a group is interacting with one of something (one phone per student), we often just use the singular form. So, gooshi is singular here.

How does the verb chek mikonand work?

This is a compound verb. It uses the English loanword chek combined with the Farsi helper verb kardan (to do). Because the subject is they (the students), the helper verb is conjugated as mikonand, giving us chek mikonand (they check).