Phial and vial are different forms of what is essentially the same word, referring to a small container for holding liquids. Both came to English in the 14th century from the same source—the French fiole, which in turn has roots in Latin—and both have appeared regularly ever since.1 Some people differentiate them in various ways—for instance, that phials are larger than vials, or that vials are for medical liquids and phials for other things—but these are not consistently borne out in general usage.
In the U.S., phial is almost nonexistent in this century, after being nearly as common as vial as recently as a century ago.2 In 21st-century British writing, meanwhile, vial became the preferred form only a few decades ago.3 Phial still seems to appear especially often in fiction, in historical writing, and in spiritual writing.
Vial is not to be confused with vile, of which it is a homophone in some parts of the English-speaking world (the U.S., at least). Vile is only an adjective. Something vile is disgusting, contemptible, or immoral.
Phial and vial
It is not known where the phials have come from but police officers said they are covered in French writing. [This is Cornwall]
Cryogenic vials stored in the vapor phase above liquid nitrogen are less likely to experience bacterial contamination. [Algal Culturing Techniques, Robert Arthur Andersen]
A phial of earth soaked in blood (presumably Dimitrios’) was discovered under the altar; similar phials were valued gifts for emperors. [Greece, Dana Facaros Linda Theodorou]
Whoever misplaced that vial has got to be having a pretty crummy day at work. [Washington Post]
He’s the only guy I know that would actually wake up and break an amyl nitrate popper under his nose. … Just twist that little yellow phial and wake up. [Life, Keith Richards]
Decorative vials of bitumen capped in cork line an oak bookcase. [National Post]
The weather was so vile play was impossible, and officials called a meeting in the clubhouse. [Independent Online]
He was a brilliant speaker, but crude in some ways, with a vile temper. And he drank. [A History of the American People, Paul Johnson]
One of the more vile things he tried to do during his Congressional romp was to abolish the National Weather Service as we know it. [Daily Kos]