It means growing phase and it is used as a fixed phrase about the new moon.
1. Luna nuova
2. Luna crescente
3. Primo quarto
4. Gibbosa crescente
5. Luna piena
6. Gibbosa calante
7. Ultimo quarto
8. Luna calante
You can read about them on Wikipedia
But it can of course also be used about other things that have a growing phase. e.g. crops, animals, children etcetera.
Growing/growth phase = fase di crescita, so we are only talking about a moon here.
In that case Duo's translation is wrong. Crescente describing the moon means "waxing" in English, i.e. the lit area is growing. The opposite is "waning" which is calante. In the Northern Hemisphere the lit side is ) = crescente and ( = calante.
The English "crescent" moon refers to the sickle shape, rather thinner than a half moon, which in Italian is luna falcata. If you want to refer to the crescent as a noun, it is la falce di luna, literally the sickle of the moon.
Hence Duo's intended version is either I: fase falcata or E: waxing phase; we can't tell which.
A moon between half and full is “gibbous” in English and gibbosa in Italian, or less technically luna scema which literally means a silly moon in the sense of "not all there". A half moon is mezzaluna (also a kitchen implement). The phase and time of full / new moon is plenilunio / novilunio.
Don't embarrass yourself if by chance you find yourself gazing at the Italian night sky with your amore. Many Italians know the vocabulary, because it is romantic.
See also Wikipedia "lunar phase".
I don't think you are wrong: https://context.reverso.net/translation/italian-english/%22fase+crescente%22
I put growing phase and it was marked correct but I have no idea what the italian is referring to. crescente also means growth or growing, "to wax" as in waxing moon translates to "crescere" so i can only assume this is an idiom? Can any native speakers help explain how and when this expression would be used ?
Vedere http://dizionari.repubblica.it/Inglese-Italiano/P/phase.php?lingua=en. Forse si potrebbe fare questa la prima destinazione per tali domande.
Si potrebbe anche trovare che https://en.wikipedia.org/wiki/Italian_grammar#Inflection_of_nouns_and_adjectives sia utile.
The phases of the moon are waxing crescent, waxing gibbous, full, waning gibbous and waning crescent, then no moon. There are thus 2 crescent phases. That's correct English usage. May not be English you know, but there are over a million words in English, and no one knows them all, except perhaps dictionary compilers. How interesting that "crescent" may come from crescere, so that waxing crescent may mean "growing growing". Ho hum, back to Italian..
I found something 1 english https://en.wikipedia.org/wiki/Lunar_phase 2 italian https://www.wikihow.it/Determinare-se-la-Luna-%C3%A8-Crescente-o-Calante
I see from the dates on the other comments posted here that this ludicrous sentence has weathered years without anyone removing or altering this ridiculous nonsense. I have to memorise the non-english of this nonsense in order to be allowed to go on with the lesson. Only by answering incorrectly can I proceed!
Oh, lighten up for heavens sake! Simply accept what they prefer and type it up to get out of this particular lesson. In fact, I appreciated Marniger's Malcomissimo's postings to get the Italian for the phases of the moon; I googled 'i fasi lunari' and have learnt a lot. Yay!!!
Fase = phase, - one of several stages something goes through
crescente = growing
Fase crescente = growing phase
This is something that can be said about e.g. the moon, or perhaps about crops on a field. In an earlier comment I have listed the Italian names of the moons different phases.