Learn Hardcore Russian: Давай договоримся о времени встречи по телефону. - Let’s agree on the meeting time by phone.

Давай is a very common conversational way to propose doing something together: Let’s … / How about we ….
It typically sounds informal and friendly. It can be used even if you’re not literally doing it “together,” but you’re suggesting a joint decision or action.

Why is it Давай договоримся and not Давай договориться?

After давай, Russian normally uses a finite verb form (conjugated as if “we” are doing it):

Давай договоримся = let’s come to an agreement (we will agree).

Using an infinitive after давай is possible in some contexts (more colloquial / different nuance), but the most standard “let’s + we” pattern here is давай + 1st person plural: давай сделаем, давай поговорим, давай договоримся.

What is договоримся grammatically (person/number/tense/aspect)?

договоримся is:

verb: договориться (to agree / to come to an arrangement)
1st person plural (we)
future tense in form, but often used with “let’s” meaning
perfective aspect, emphasizing reaching an agreement as a completed result (not the process of negotiating).

Why is the verb perfective (договориться) and not imperfective?

Because the goal is a result: to arrive at an agreed time. Perfective fits “let’s settle it / let’s agree on it.”
If you used an imperfective idea, it would lean more toward an ongoing process like “let’s discuss/coordinate,” but договориться specifically points to successfully reaching agreement.

Why is it о времени? What case is времени and why?

о (about) requires the prepositional case.
So время becomes о времени (about the time).
This is a standard pattern: говорить о чём-то, думать о чём-то, договориться о чём-то.

What does встречи mean here, and what case is it?

встречи comes from встреча (meeting) and is genitive singular here.
время встречи is a fixed “noun + noun” relationship meaning the time of the meeting (literally “time (of) meeting”). Russian often uses the genitive for this “of” relationship.

Is о времени встречи one chunk? Could it be phrased differently?

Yes, о времени встречи is one unit: about the meeting time.
Common alternatives:

о времени нашей встречи = about the time of our meeting (adds нашей)
о времени, когда встречаемся = about the time when we’re meeting (more conversational)
о времени для встречи can sound more like “a time suitable for a meeting,” but is less direct than время встречи.

Why is it по телефону and not по телефону́ or по телефону́? (Which stress is correct?)

The standard stress is по телефо́ну (stress on -фо́-).
So: Давай договори́мся … по телефо́ну.
(Stress matters in Russian; the written form doesn’t show it, so it’s a common learner question.)

What does по телефону literally mean, and what case is телефону?

по телефону means by phone / over the phone.
телефону is in the dative singular. The preposition по has several meanings, and with communication/means it commonly takes dative: по телефону, по почте (by mail), по интернету (via the internet, though usage varies), etc.

Could I say по телефону at the beginning or in a different place? How flexible is the word order?

Word order is fairly flexible:

Давай договоримся по телефону о времени встречи. (very natural)
По телефону давай договоримся о времени встречи. (emphasis: “by phone”)

The original order feels neutral: first the proposal (давай договоримся), then what you’ll agree on (о времени встречи), then how (по телефону).

Is Давай polite enough? What if I’m talking to someone formally?

Давай договоримся… is informal (fine with friends, peers).
For formal/polite situations, use:

Давайте договоримся о времени встречи по телефону. (давайте = polite/plural)
Or even more formal:
Давайте согласуем время встречи по телефону. (to coordinate/confirm)
Предлагаю согласовать время встречи по телефону. (I suggest we coordinate)

Do I need to specify “with whom” we’re agreeing? Can договориться take another object?

Often context makes it clear, but you can specify the person using с + instrumental:

Давай договоримся с ним о времени встречи по телефону. = Let’s agree with him on the meeting time by phone.

So the common patterns are:

договориться о чём? (about what)
договориться с кем? о чём? (with whom, about what)