Shouldn't “some of the phenomenon” be plural?

…some of the phenomenon…

Consider that usage as a typo, it's like criteria vs criterion, many use the former thinking it is an uncountable noun while other speakers add an "s", i.e. criterias, to make it plural.

The study of Greek and Latin does not enjoy the same prestige as it used to in the past, so we shall hear the following with increasing frequency: phenomenons and datas and agendas in the future.

The OED‘s evidence shows that the plurals datas (first recorded in 1645) and medias (appearing in 1927) have a long history and crop up in varied sources, from scientific and academic journals to The Times.

Oxford Dictionaries Blog

I found this 2011 article in the Daily Telegraph, an exemplary hodgepodge, but at least both forms are recognizable as being plural.

Weird weather: the top ten strangest phenomenons

Scientists now believe that tiny bugs in the earth's atmosphere can cause storm clouds to form. Here is a list of 10 other amazing weather phenomena