ooyasan ni denwasite, kagi wo uketoru zikan wo kimemasita.

Because に marks the person the action is directed toward.

In 大家さんに電話して, the action is 電話する, and the landlord is the person being called, so に is used.

• 大家さんに電話する = to call the landlord
• 友だちに電話する = to call a friend

With 電話する, Japanese normally uses に for the person you call.

電話して is the て-form of 電話する. Here it links two actions into one sentence:

1. called the landlord
2. decided on a time

So the sentence has the pattern:

Aして、Bました
= did A, and then did B

This often suggests sequence, so it feels like:

• I called the landlord, and then
• I decided on a time to receive the key

Only the final verb, 決めました, carries the past polite ending for the whole sentence.

Yes, 電話して comes from 電話する.

• dictionary form: 電話する
• て-form: 電話して

You may also hear 電話をする, since 電話 is originally a noun plus する. But in everyday Japanese, 電話する is extremely common, and 電話して sounds completely natural.

So:

• 大家さんに電話して = natural and common
• 大家さんに電話をして = also possible, but a bit less compact

This is a noun-modifying clause.

Japanese often puts a whole verb phrase directly before a noun to describe it.

So:

• 鍵を受け取る = receive the key
• 時間 = time

Together:

• 鍵を受け取る時間 = the time to receive the key / the time when I will receive the key

In English we often need words like when, to, or for, but Japanese does not. The verb phrase simply comes before the noun.

Because before a noun, the plain form is often used to describe that noun in a neutral way.

Here, 鍵を受け取る時間 means the time for receiving the key or the time when the key will be received. It is not mainly focusing on past tense. It is identifying what kind of time it is.

If you used 受け取った時間, that would usually mean the time when someone received it, referring to an already completed event. That is a different meaning.

So in this sentence, 受け取る is the natural choice.

Because Japanese relative clauses do not need a word like that, when, or to between the verb and the noun.

English:

• the time to receive the key
• the time when I receive the key

Japanese:

• 鍵を受け取る時間

That whole verb phrase directly modifies 時間.

This is a very common Japanese structure:

• 日本で買った本 = the book I bought in Japan
• 明日会う人 = the person I’ll meet tomorrow
• 鍵を受け取る時間 = the time to receive the key

Because 時間 is the direct object of 決めました.

What did the speaker decide?

• 鍵を受け取る時間 = the time to receive the key

So:

• 時間を決めました = decided the time

The を is not connected to 受け取る. That verb already has its own object:

• 鍵を受け取る = receive the key

Then the entire phrase 鍵を受け取る時間 becomes the thing that was decided, so it takes を before 決めました.

The subject is omitted because Japanese very often leaves out information that is clear from context.

The sentence does not explicitly say I or we, but in many situations the natural understanding is something like:

• I called the landlord and decided on a time to receive the key.

Japanese often sounds more natural when the subject is not repeated unnecessarily.

If needed, a subject could be added:

• 私は大家さんに電話して、鍵を受け取る時間を決めました。

But in ordinary conversation, leaving it out is very common.

Yes, that is the most natural reading.

電話して、決めました usually suggests:

1. first, the speaker called the landlord
2. then, as a result, they decided on a time

The て-form can connect actions in several ways, but in this sentence the sequential reading is the most straightforward.

This is a very useful distinction.

• 決めました = decided
• 決まりました = was decided / got decided / was settled

In this sentence, 決めました shows that someone actively made the decision.

• 時間を決めました = I/we decided on the time

If you said:

• 時間が決まりました

that would mean:

• the time was decided
• the time got settled

So 決めました focuses on the person doing the deciding, while 決まりました focuses on the result.

大家さん here means landlord or landlady.

The reading is おおやさん, not the more obvious Sino-Japanese-style reading you might expect from the kanji. This is one of those words whose reading simply has to be learned as vocabulary.

The さん is the normal polite suffix attached to a person, so 大家さん is the ordinary polite way to refer to a landlord.

It is polite, but not extremely formal.

The final verb 決めました uses the -ます form, which makes the sentence polite. That is standard everyday polite Japanese.

Also, 大家さん is a polite way to refer to the landlord.

So the overall tone is:

• natural
• polite
• appropriate for everyday conversation

A casual version would be:

• 大家さんに電話して、鍵を受け取る時間を決めた。

Yes, that is a very natural way to understand it.

Even though the sentence literally breaks down as called the landlord and decided the time to receive the key, the overall idea is often:

• arranged a time to pick up the key
• set up a time to receive the key
• agreed on a time for getting the key

Japanese often expresses this kind of practical arrangement in a straightforward, literal way, while English may use a smoother phrase like arranged a time.