Punctuation Marks and Etc. of the English Language

@Robin2

English is your mother tongue which you have acquired in a very natural way; later on, you cultured the language and have possessed a good control on the flow of the language.

I am a non-native, and I have learnt the English Language through hard practice of the syntax and semantics rules of the language. Therefore, it is totally forbidden for me to enter into any kind debate on the English Language structure with a native.

However, I (we) as a non-native(s) always apply the rules/conventions of the English language in the analysis of a sentence. The rules/conventions are the products of the English Linguists.

In a beginner/teaching environment, portability is desirable.

Analysis:
(1) The sentence has two parts: an introductory phrase and the independent clause.
(2) When a sentence begins with an introductory phrase, the phrase is to be punctuated by a comma (,).

Now the question: Is 'In a beginner/teaching environment' a phrase? The typical definition of a phrase is: a small group of words standing together as a conceptual unit, typically forming a component of a clause. Does this definition of phrase stand in favor of saying that 'In a beginner/teaching environment' is a phrase?