The informal rule is a stylistic one. Keep the complement as close as possible.
That really helps me out.
Clearly this is not a lot of separation, and to phrase it "helps out me" would sound awkward and awful.
That really helps out the children who are starving every day in Africa.
To put "out" at the end would simply require the reader or listener to wait too long to parse your verb as a phrasal verb.
To sum it all up: it's a judgment call.
To sum up everything I have stated in this response: it's still a judgment call.
As noted in the comments, phrasal verb is a slippery term that has been variously defined. Indeed, the Cambridge Grammar of the English Language states (p274): We do not use the term 'phrasal verb' in this grammar.
However, if we follow the definition given in the foreword of the Collins Cobuild Dictionary of Phrasal Verbs, then phrasal verbs are "combinations of verbs with adverbial or prepositional particles".
So the answer to your question: "When is a phrasal verb not followed by a preposition?" is "When it is followed by an adverb(ial)." For example: to steal away, to cut back.
Other phrasal verbs have particles which can in other contexts function either as an adverb or as a preposition: to put down, to get across, to come about.
The last group contains particles that can only function elsewhere as prepositions: to make do with, to get at, to make of.
The question in your title is a complex one. The textbook that you refer to should be able to help you answer it.
Best Answer
Both ‘hold up’ and ‘hold on’ can be used to ask someone to wait.
(www.differencebetween.net)