As a general rule I know that I should maintain consistency if I choose some style, etc.
But I am not sure about this: Is it acceptable to use the phrase "For example" and "e.g." interchangeably in the same text?
TLDR: Technically not, but effectively yes. When it is not acceptable, a minor modification makes it acceptable.
Generally, when it is acceptable to use "for example", it is acceptable to use "e.g.", with two caveats.
Firstly, as a native (American) English speaker, I never use "e.g." in spoken communication. It is also more often used in more formal or academic contexts, because it is an initialization of the Latin phrase "exampli gratis", which literally translates as "for the sake of example".
Secondly, in my experience, the exact placement and usage tend to differ; specifically "for example" can be used in a subordinate clause after the main clause (see example #1 below) or at the beginning of the following sentences (see example #2 below). "E.g." is only used in a subordinate clause(see example #3 below), but if "for example" is used at the beginning of the next sentence, one can generally combine the two sentences into one with "e.g." (unless the "For example" sentence begins a new paragraph). Some people will enclose their example(s) in parentheses (see example #4 below), especially if the list of examples are long, or the sentence continues with more clauses after the examples.
I enjoy reading long books, like The Lord of the Rings, for example.
I enjoy reading long books. For example, I enjoy reading The Lord of the Rings.
I enjoy reading long books, e.g. The Lord of the Rings.
I enjoy reading long books (e.g. The Hobbit, The Fellowship of the Ring, The Two Towers, The Return of the King, The Wheel of Time series) because I don't like having to look for a new book to read.
This is a matter of style. Under some style guides you might have to. For example, APA says that "e.g." should be used inside parentheses and "for example" outside:
Other standard Latin abbreviations should also be used in parentheses rather than written out:
- e.g. for for example (e.g., the Imperial traffic stop failed to apprehend the runaway droids)
Here is a nice chart of this information.