To correct myself . . .

MJR> English is also full of phrasal verbs (verb +
MJR> preposition[s]), which are transitive when treated
MJR> as a unit

So far, so good . . . .

MJR> but officially analyze into an intransitive
MJR> verb modified by a prepositional phrase: "look at",
MJR> "climb up", "watch out for", etc.

Not so much; I chose my examples poorly.  "He looked at X" and "
She climbed up X" can sensibly be analized as "At X is where he looked"
and "Up X is where she climbed".  "Watch out for" is actually a
phrasal verb "Watch out" modified by the preposition "for".

SS> I'm not sure I agree; look at these two sentences:

SS> Louise looked up Teresa's phone number.
SS> Louise looked up Teresa's nose.

Much better example.

PhD> I've always considered these "phrasal verbs" to be
PhD> "verb + adverb" rather than "verb + preposition."

Most can be analyzed that way, but I believe there are also some that
can be interpreted as prepositions rather than adverbs.  Naturally, I'm
completely failing to think of any examples at the moment.

PhD> 5. ?George is the maker-upper of the game.

PhD> 6. ?George is the maker-up of the game.

PhD> 7. *George is the upmaker of the game.

PhD> Many people say sentence 5 in conversation, although
PhD> sentence 6 makes more logical sense. In writing, a
PhD> circumlocution such as "the one who made up the
PhD> game" is used. Sentence 7 would be very natural
PhD> if the verb were "upmake" rather than "make up."

In this example, I would bypass the difficulty by saying that George is
the creator of the game.  :) But this has come up before, and let me repeat
what I said then: I consider your #7 - albeit hyphenated as "up-maker" -
perfectly natural, correct, and appropriate for a formal register.
Informally, I would tend to emit #5, but with a self-conscious air of