Learn Italian: L'inizio del progetto è la fase più difficile. - The beginning of the project is the most difficult phase.

L'inizio is the noun form, meaning "the beginning". The verb form is iniziare (to begin). If you wanted to express a similar idea using the verb, like "The project has begun", you would use the auxiliary verb essere because the project is changing states on its own: Il progetto è iniziato.

Why is the word order la fase più difficile instead of putting più difficile before the noun?

In English, we say "the most difficult phase", putting the superlative before the noun. In Italian, you almost always put the noun first, followed by più and the adjective. Literally, the structure is "the phase most difficult".

Fase ends in -e, so how do we know it uses the feminine article la?

Nouns ending in -e in Italian can be either masculine or feminine, so you just have to memorize their gender when you learn them. Fase (phase) happens to be feminine, which is why it takes the feminine article la.

If fase is feminine, why doesn't the adjective change to difficila?