Learn Italian: La fase operativa è già cominciata. - The operational phase has already begun.

Cominciare is a verb that can take either avere or essere depending on how it's used. When it has a direct object (someone begins something), it uses avere. But here, the subject itself is just doing the action without an object receiving it (La fase operativa is beginning), so it uses essere.

Could I use "avere" if I rephrased the sentence to include a person starting the phase?

Yes! If you change the sentence so that someone is actively doing the starting, cominciare takes a direct object and switches to using avere. For example: Abbiamo già cominciato la fase operativa (We have already begun the operational phase).

Why does the past participle end in "-a" (cominciata)?

Because the auxiliary is essere, the past participle must agree in gender and number with the subject. The subject here is La fase (feminine singular), so the default cominciato changes to cominciata.

Why is già placed between the auxiliary (è) and the past participle (cominciata)?

In Italian, short adverbs of time like già (already), ancora (yet/still), and mai (ever/never) are usually placed right between the auxiliary verb and the past participle.