Well, I don't know english enough to know what's the difference between a sentence and a phrase. "Phrase" means "sentence" in French... so I assume that "Phrase" is a synonimous of "sentence" but of course I may be wrong.
Well at least, "to begin" and "to commence" are synonimous... with the first one having a germanic root when the other one have a French root (French verb "commencer").