La fase dura due giorni.

Because fase is a feminine singular noun in Italian, so it takes the feminine singular definite article la.

A useful thing to remember is that nouns ending in -e can be either masculine or feminine, so you often have to learn the gender together with the noun. Fase happens to be feminine:

• la fase
• le fasi

Here dura is a verb, not an adjective.

It comes from durare, which means to last.
So dura is the third-person singular present tense form:

• io duro = I last
• tu duri = you last
• lui/lei dura = he/she/it lasts

In this sentence, la fase is singular, so the verb is dura:
La fase dura due giorni.

Yes. Duro/dura can also be an adjective meaning hard, tough, or severe, depending on context.

For example:

• una prova dura = a hard test
• un periodo duro = a tough period

But in La fase dura due giorni, it is clearly the verb durare because it is followed by a length of time: due giorni.

Because with durare, Italian normally gives the length of time directly, without a preposition.

So you say:

• La fase dura due giorni.
• Il film dura due ore.
• La riunione dura mezz’ora.

This is similar to English lasts two days, where no extra preposition is needed after lasts.

It is much more natural to say La fase dura due giorni.

With durare, Italian usually prefers the duration without per.
Adding per is generally less standard or less natural in a basic sentence like this.

So for learners, the best rule is:

• with durare → usually no per
• dura due giorni, not normally dura per due giorni

Because the sentence says two days, and due is more than one.

The singular is:

• un giorno = one day

The plural is:

• due giorni = two days

So:

• La fase dura un giorno.
• La fase dura due giorni.

Because in Italian, when you give a quantity like two days, you normally do not use an article before the number.

So you say:

• due giorni
• tre settimane
• quattro ore

not:

• i due giorni in this sentence

I due giorni would mean the two days, which is more specific and would be used in a different context.

This is the normal, neutral word order:

subject + verb + duration

• La fase = subject
• dura = verb
• due giorni = duration

Italian word order can sometimes change for emphasis, but this version is the most natural and standard for a learner.

Fase usually means phase or stage, depending on context.

So it can refer to:

• a stage in a process
• a phase of a project
• a period in development

English often uses both phase and stage, but Italian uses fase in many of the same situations.

It can often refer to a current fact or a planned/general duration.

Italian, like English, often uses the present tense for things that are generally true or part of a schedule or plan.

So La fase dura due giorni can mean something like:

• this phase lasts two days
• the phase is two days long
• the phase will last two days

The exact time reference depends on context.

If you want to talk about more than one phase, both the article, noun, and verb must change:

• La fase dura due giorni. = The phase lasts two days.
• Le fasi durano due giorni. = The phases last two days.

Changes:

• la → le
• fase → fasi
• dura → durano

A simple pronunciation guide is:

la FA-zeh DOO-ra DOO-eh JOR-nee

A few points:

• fase has stress on fa
• dura has stress on du
• giorni sounds roughly like JOR-nee
• gi before o sounds like the j in job

A more approximate full pronunciation is:

lah FA-zeh DOO-rah DOO-eh JOR-nee