This sonata starts with 8 symmetric 4 measure phrases, which is the A section. I think the A section functions as a phrase group, because none of the phrases really end in a conclusive way. Although each phrase ends in PAC's (changes keys to A Major every other phrase),each phrase seems very unsure and uneasy. It also is in open binary form because is ends in a different key than what it starts out in. The rhythmic structure is exactly the same for each phrase, and doesn't change very much. There are a lot of dynamic changes in this piece, which adds to the structural phenomena.
The B section is really developmental, because it takes the motive and really varies it: it feels unstable, like it's building up to something bigger. It playes around with different keys as well. At measure 48 it goes right back to the expository section of the A, and then ends in the same key we started in, D Major(which equals rounded binary form!). It's more dramatic this time, and significantly louder.