As a native French speaker who hadn't read this word before, I intuitively give it the meaning “to make sentences that are somewhat pompous and are not as interesting or important as their authors believe”.
-(i)buler is not a common or productive suffix. I'm not counting -i- as part of the suffix because it's a natural faux-Latin back-formation from phrase: many Latin roots have a weak e/i ending that becomes i when there's a following consonant (such as in the suffix -(i)ble indicating possibility) but is omitted altogether when it's at the end of the root. The only suffix that's truly recognizable here is -er, which is a generic verb suffix. In other words where it occurs, the -bul- part is part of the root ((af)fabuler < Lat. fabula, déambuler < Lat. ambulare, tabuler < Lat. tabula are the only common verbs with a root ending like this).
None of these words are close enough to make phrasibuler appear as a compound of phrase and another word. The word does however vaguely remind me of volubile (loquacious). So someone who phrasibule probably talks a lot, but what they say may be uninteresting or garbled. I'm also reminded of patibulaire, an adjective which means that a person looks like a criminal, so the words of someone who phrasibule are probably to be condemned.
I'm also reminded of a later nonsense word zibule¹. (By humorists Pierre Dac and Francis Blanche in the 1960s, part of a joke about cintre à zibule. Cintre is a clothes hanger. “À zibule” can either be parsed as Zibule being the inventor of the hanger — Zibule's clothes hanger — or zibule being an accessory of the hanger — originally the hook part, but it can refer to the horizontal bar among younger generation.). I don't know why the word was chosen, but it's an example of the sonority -ibule working well for a nonsense word.
Making a verb more complex than it should be, with a pejorative result, is a rare but not isolated phenomenon in French. I'm reminded of the suffix -coter which can indicate that something is more complex than it should be, found naturally in tricoter (knitting, with a common figurative meaning of constructing something complex, often in a pejorative way) and in deliberate coinages such as emberlificoter and tarabiscoté.