I stress that like this: [3gɛt̬ 2ɔf jər 1hɑɪ 3hoərs]. I've used "1" for primary stress,
"2" for secondary, and so on. As you say, the "t" of "get" is flapped -- that is independent of the stresses of neighboring vowels, because the "t" is at the end of a syllable and is between vowels. (I don't understand the diacritic you've put on the [t].)
If by "linked" you mean the "t" becomes part of the first syllable in the next word, no, that does not happen here. That would prevent flapping the "t".
Perhaps "high horse" has more stress on "high" because in this idiom, it's a compound (that's what it feels like). Elsewhere, not in the idiom, I'd have "2high 1horse", which as you say would be the ordinary stress of an adjective modifying a noun.
I suppose "get off" should count as a phrasal verb, since it's a phrase and is a verb. It does have more stress on the "off" (which, however, doesn't seem to be a particle of the sort that goes with verb-particle constructions, because it doesn't move to the right of a following object -- *"Get your high-horse off").