This whole "build Phase 1 now and build Phase 2 later" has quite a few parallels to Ottawa, although in Ottawa's case, the BRT already exists. Many in the west end were against the LRT project, because Phase 1 stopped at Tunney's Pasture (not very west end at all). But Phase 2 will extend the line to Baseline and Bayshore.
Phase 1 in Ottawa is scheduled to open in early 2018, with the Western LRT extension in 2020 or 2021. Hopefully, with the Cambridge extension study starting soon, Waterloo Region can have a similar gap between Phase 1 and Phase 2 openings. The last thing you want, especially if you're in Cambridge and a supporter of the LRT project, is to see Phase 1 open and see Phase 2 sitting on a shelf somewhere.