Like most words, space has more than one meaning, and we must use contextual reasoning to work out which is intended.
You're thinking of the meaning of space which is a mass noun: that is, uncountable, which is why the article seems misplaced to you.
For example, this is how Merriam-Webster (MW) defines the uncountable space you're thinking of:
space (n, uncountable): the boundless three-dimensional extent in which objects and events occur and have relative position and direction
However, it is the very presence of the article in your text which serves as a clue that that's not the definition being employed here.
To the contrary, because there is an article, the intended meaning must be some kind of count noun. Thus, we refer back to our dictionary, and look for definitions of space which not only fill that role in the sentence (i.e. be count nouns), but also make sense in context.
To remind us of the context:
A person who suffers from claustrophobia has a dread of being confined in a small space,
So the space under consideration must be limited (or the claustrophobe could not be confined to it), and it must be possible to have more than one of them (again, the article establishes that we're dealing with a count noun).
So, returning to Merriam-Webster:
space (n, countable): an area that is used or available for a specific purpose
That looks quite suitable: first, it is a count noun, because it's described as an area (did you notice that area can be a count noun too?), and second, it is set aside for some particular purpose, which in our case, is to confine the claustrophobe.
We can get further corroboration by looking at the subordinate glosses:
a limited extent in one, two, or three dimensions : distance, area, volume
an extent set apart or available
Again, we see articles before extent in both subdefinitions, and now we're explicitly told that the space is both set apart and, crucially, limited. That is, it's capable of being small.
The key takeaway here is not that space can take an article sometimes, but the more important lesson that when you're surprised or confused by a particular usage, it's always best to first check a dictionary to see if there are any senses for the word you were previously unaware of.
And I can tell you that this happens even to native speakers, and we use the same strategy. Surprised (baffled!) that anymore can be used in a positive context? Check a dictionary and learn that one of its meanings is nowadays.
The key to successful business development in this industry is understanding the market from a regional perspective as Canada is a large country with different local dynamics.
successful business development is an unspecific activity, so no article is used.
regional perspective is one of several possible perspectives (views), so I would use a.
dynamics is plural, so no article.
The proof of their success is evident in acquisition interest by larger players and ongoing creation of smaller companies by their former employees.
interest here would be one of several "interests", or "interest" in general. So optional article use here.
larger players and smaller companies are plural so no article.
Best Answer
There is no reason to think that "audience" is being treated as plural in the sentence, so why would you object to a / an? (I assume you've come across "a family", "a group", "a class", "a school", "a government", "a team".)
However, even when collective nouns are treated as plural, they can still take the indefinite article a / an. We could say, for example, "when an audience are happy with a performance, they often applaud", "when a government are disunited, the opposition often benefits", or "when a couple are fighting, their children often notice".
From Kevin Bridges in The Guardian, 15th October 2014:
From Clare Dyson, AusDance, 2008:
Jodie Helm quoted in Caroline Heim's Audience As Performer, 2016:
Is your misconception that collective nouns can't take the indefinite article perhaps based on a confusion between collective nouns and mass nouns? These are two different things. "Audience" is almost always a countable noun (and according to Oxford, the use of "audience" as a mass noun is archaic). It is true that mass nouns can't take the indefinite article (although many mass nouns can be treated as countable under certain circumstances, often with a slightly different meaning - and when treated as countable, they can take the indefinite article - e.g. "a cheese" meaning "a type of cheese").