Halliday & Matthiessen (2014: 414):
In the case of see off and many other phrasal verbs, the phrasal verb is thus not agnate with a non-phrasal counterpart. For example, there is no systemic proportionality such that see is related to see off as sound is to sound off. However, with many verbs, the simple verb is agnate with the combination of verb + adverb, e.g. break ~ break off (‘separate’), kill ~ kill off (‘kill in large numbers, rendering extinct’), take ~ take off (‘remove (clothing)’), beat ~ beat up (‘beat severely, inflicting injury’), drink ~ drink up (‘drink to the last drop’), go ~ go up (‘ascend’), go ~ go on (‘continue going’), although specialised senses may also evolve, as with break off in the sense of ‘abruptly stop talking’, beat up in the sense of ‘drum up support’, and go on in the sense of ‘talk at great length’.