What is the analysis of that phrase?

If you look at the very long thread on the analysis of Sonnet 18, you will find that there already has been considerable discussion on this particular line.

We sais that it can be considered as an adverbial phrase, but why?

It tells something about an action. That is, it modifies a verb.

And every fair from fair sometime declines. (This is the action. It's something that happens.)

Your adverbial phrase tells how it happens.

What does it do? It declines.

How does it decline? By chance, or nature's changing course untrim

6. And often is his gold complexion dimm'd;
7. And every fair from fair sometime declines,
8. By chance or nature's changing course untrimm'd;

So are these all adverbial phrase?

No. Only the prepositional phrase on line 8. The others are main clauses.

6 & 7 are simple actions.

Sometimes the sun grows dim.

Sometimes beautiful things grow ugly.

" And every fair from fair sometimes declines" is from fair a prepositional object?
" Nor lose possession of that fair you own" is that fair a prepositional object?
in Skakespere we find this words order " When in eternal lines to time thou grow'st" is when in position of topic? If I consider x bar schema is it in the spec of cp?? and" in eternal lines to time "is the prepositional object?

Mario Rossi" And every fair from fair sometimes declines" is from fair a prepositional object?

"from fair" is a prepositional phrase. From is a preposition and "fair" is the object (or complement.)

Mario Rossi" Nor lose possession of that fair you own" is that fair a prepositional object?

"of that fai

Perfect, if I consider line 4 " and summer's lease has all too short a date"... can "all too short a date" be an adverbial object?? and in " Sometimes the eye of heaven shines too hot" considering that this is an adverbial phrase that starts with a frequency adv , "too hot" can be adjectival predicate?

Tnks

"As long as man can breath or..." is correct to say that is an adverbial phrase because as long as can be consider adv?if I have "This gives life to thee".. to thee can be indirect object and life direct or is all direct? cause I know that thee is used as (objective-accusative) and it's an archaic form...