What is the phraseology when leaving a TRSA?
You can say "cancel radar service" (probably the most standard under ICAO), "cancel flight following," "request frequency change," or anything else that conveys the same general idea. If all else fails, plain English is always acceptable too.

Regardless of which you say, ATC's response should be "radar service terminated, squawk VFR, frequency change approved," same as in any other class E airspace.