Halliday & Matthiessen (2014: 415-6):
The experiential configuration [i.e. phrasal verb serving as single Process] is reflected in the thematic variation. If the prepositional phrase for a needle was a circumstantial element it should be able to be thematised; but we do not say for that I’ll look; the more likely form is that I’ll look for. Similarly with the adverbial ones: see off is a single process, so whereas we would say there I’ll see John (= I’ll see John there but with there instead of I as Theme), there is no form off I’ll see John thematically related to I’ll see John off.