Minä aion korjauttaa puhelimeni ensi maanantaina, koska näyttö on taas rikki.

Yes, minä can be omitted.

Finnish usually does not need subject pronouns when the verb form already shows the person:

• (Minä) aion = I intend / I’m going to
• The ending in aion already tells you the subject is I

So:

• Minä aion korjauttaa puhelimeni...
• Aion korjauttaa puhelimeni...

Both are correct.

Using minä can add:

• emphasis
• contrast
• slightly more explicit or careful style

For example, Minä aion... can feel a bit like I am going to... as opposed to someone else.

In everyday Finnish, leaving it out is very common.

Aion is the 1st person singular of aikoa, which means to intend, to plan, or to be going to do something.

So:

• aion korjauttaa = I intend to have repaired / I’m going to have repaired

Finnish does not have a separate future tense like English does. Instead, it usually uses:

• the present tense
• time words
• verbs of intention like aikoa

That is why Finnish can express the future with a present-tense verb:

• Aion... = I’m going to...
• ensi maanantaina = next Monday

Together, these clearly place the action in the future.

This is a very important point.

• korjata = to repair / fix
• korjauttaa = to have something repaired, to get something repaired, or more literally to cause someone to repair something

So the sentence means that the speaker is not necessarily fixing the phone personally. Instead, they plan to take it somewhere or arrange for someone else to fix it.

Compare:

• Korjaan puhelimeni. = I will repair my phone myself.
• Korjautan puhelimeni. = I will have my phone repaired.

The ending -ttaa / -ttää is often used to form this kind of causative verb.

Puhelimeni means my phone.

It consists of:

• puhelin = phone
• -ni = my

So:

• puhelimeni = my phone

You can also say:

• minun puhelimeni = my phone

But in Finnish, the possessive suffix -ni often makes the separate pronoun minun unnecessary.

Why puhelime- in the middle?

The noun puhelin changes its stem before many endings:

• basic form: puhelin
• stem used here: puhelime-
• • ni → puhelimeni

This is a normal noun pattern in Finnish.

Here puhelimeni is the object of the verb korjauttaa.

In many Finnish sentences, a complete object in the singular often looks like the genitive:

• korjaan puhelimen = I repair the phone

But when a possessive suffix is added, the form changes:

• korjaan puhelimeni = I repair my phone
• korjautan puhelimeni = I have my phone repaired

So although puhelimeni does not end in -n, it can still function as the singular total object.

This is one of those places where Finnish form and function do not match English very neatly, so it is best to learn puhelimeni here as the normal correct form.

Ensi maanantaina means next Monday.

The word maanantaina is in the essive case, which often answers the question when? with days and dates.

So:

• maanantai = Monday
• maanantaina = on Monday

And:

• ensi maanantaina = next Monday

Some other similar examples:

• tiistaina = on Tuesday
• perjantaina = on Friday
• ensi perjantaina = next Friday

Notice that ensi itself does not take the case ending here; the case shows up on the noun:

• ensi maanantaina
• not ensinä maanantaina

In many contexts, ensi maanantaina means next Monday / the coming Monday, but real-life usage can sometimes feel a little context-dependent.

In standard learner-friendly usage:

• ensi maanantaina = next Monday

If the speaker wants to be especially clear, they may add more context.

This is similar to how English speakers may not always agree perfectly on this Monday vs next Monday. Finnish can have a similar practical ambiguity in conversation, but ensi maanantaina is the normal way to say next Monday.

Koska means because in this sentence.

So:

• ..., koska näyttö on taas rikki.
• ..., because the screen is broken again.

Be careful: koska can also mean when in some contexts.

Examples:

• Tulen, koska voin. = I’m coming because I can.
• Koska tulet? = When are you coming?

So the meaning depends on context. In your sentence, it clearly means because.

Because koska näyttö on taas rikki is a subordinate clause.

Finnish normally separates a main clause and a subordinate clause with a comma:

• Minä aion korjauttaa puhelimeni ensi maanantaina, koska näyttö on taas rikki.

Main clause:

• Minä aion korjauttaa puhelimeni ensi maanantaina

Subordinate clause:

• koska näyttö on taas rikki

This is very standard Finnish punctuation.

Taas usually means again.

In this sentence:

• näyttö on taas rikki = the screen is broken again

It often suggests repetition, and sometimes it can also carry a slight feeling of annoyance, depending on tone:

• again
• once again
• yet again

So here it may imply that this is not the first time the screen has been broken.

A related word is uudestaan, which also means again, but it is more often used for doing an action another time, while taas is very common for repeated situations or states.

Rikki means broken.

In sentences like this, it is used with olla (to be) to describe the condition of something:

• Näyttö on rikki. = The screen is broken.
• Puhelin on rikki. = The phone is broken.

It does not behave exactly like a typical adjective in every respect, so many learners find it easiest to learn it as a common fixed expression:

• olla rikki = to be broken

That is the most useful way to remember it.

Because näyttö is the subject of the clause:

• näyttö = the screen
• on = is
• rikki = broken

So:

• näyttö on rikki = the screen is broken

The form näytön is usually the genitive form and would not fit as the subject here.

This clause follows a very basic Finnish pattern:

• subject + verb + complement
• näyttö + on + rikki

The word order here is natural and neutral, but Finnish word order is more flexible than English word order.

Neutral order:

• Minä aion korjauttaa puhelimeni ensi maanantaina, koska näyttö on taas rikki.

You can move elements around for emphasis, for example:

• Ensi maanantaina aion korjauttaa puhelimeni, koska näyttö on taas rikki.

This puts more focus on next Monday.

However, the original order is a very good standard pattern for learners:

• subject
• verb
• object
• time expression
• reason clause

So yes, word order can change, but the sentence as given is a very normal and natural version.