Is it a bad idea to lift phrases straight from my query and use them in my synopsis? (Would I have to sue myself?) Or should I make up new ways to say the same things?
Your query, presumably, includes a two or three paragraph description of your book. You missed your kid's soccer game and the Wimbledon semi-finals to write it, and you like it. It's perfect, each word specifically chosen for its ability to call out to an agent like cheesecake to John Travolta. To change a single word would be akin to Keats converting his "Ode on a Grecian Urn" to a limerick.
Now the agent wants a three-page synopsis. You'd like to include a few of your better lines from the query in the synopsis, but you fear the agent will think, Man, that sounds familiar. This guy's either so lazy he cut and pasted a paragraph from his query into his synopsis, or he stole it from someone else's query. The last thing I need is another Kaavya Viswanathan situation. That chick almost ruined me.
If you sent a query and have now had a request for a synopsis, I wouldn't worry about this at all. If you're putting both query and synopsis into the same envelope, however, you might take into account the fact that the agent will have just read your query, and adjust the synopsis accordingly. Agents have notoriously short attention spans. If you cover the same ground twice they may decide to move on to something that sounds more original.