I'm agreeing with Jami that "to call" is tricky because the "to" is part of an infinitive form of a verb, rather than a preposition. In this sentence, "to call" functions as the direct object of the verb "tried." I think it's hard because the whole phrase is bolded as if it's one phrase, but that isn't how I look at it (I guess that's why the answers are wrong?).
Some clues to prepositional phrases (besides the word "to") are that they usually work with nouns (things you can "have") and they usually tell where or when type things. Your Applications book should have a list of those where/when/what types of question clues (You tried? Tried what? Oh, you tried to call...). Also, I always remember that the Chinese don't use prepositions, so they have to figure out whether something is on, under, or over the table, or whether something is "to" or "from," just by the context, so that always helps me remember prepositions, and it would be a clue that "to call" would NOT have one of those missing Chinese words but "to the end of the road" would. Oh, well, I guess I have my own weird ways of remembering things LOL.
I'm not sure about the Logic of English as a grammar reference (isn't it a spelling program?) but I do like all the online grammar resources that are available these days. Purdue's site has infinitive phrases if you scroll down this page: https://owl.english.purdue.edu/owl/resource/627/03/
Or, there are specifically grammar reference books, as well.
My goals for my son in 8th grade had to do with introducing all the yucky phrases and such, so that if his sentences in high school weren't working, we could find a way to talk about them. I didn't care if his reaction in high school was "oh, that's because of one of those phrasey things," I just didn't want him to say "no clue what language you are speaking." Each family's goals will differ, of course, but the tests aren't a big part of the grade (and don't have to be graded at all, if you don't like