(ATCO here) I find half the battle with RT is remembering the phrases, the other half is the reaction your brain has when it hears you saying something that it thinks sounds daft. I overcame both of these by practicing saying the phrases out loud, first from a sheet and then from memory. Try using the CAP413 and getting a mate to read out the controller bits, with you replying. Oh and a top tip: if you can't remember the standard phrase (or there isn't one), it's no problem to use normal English as long as it is clear and concise.