The inaugural season of the Symphony of the Seas will be spent in the Mediterranean. Following an inaugural season in the Mediterranean, the Symphony of the Seas will reposition to begin cruising from Miami, Florida. The ship's primary deployment from Miami will be 7 Eastern or Western Caribbean cruises that depart on Saturdays.
In preparation for the Symphony of the Seas, a new cruise terminal is being built in Miami, Florida. This cruise terminal is expected to open in October 2018 prior to the Symphony of the Seas' arrival. Once built, the Allure of the Seas will use this cruise terminal too. Royal Caribbean's press release says the cruise terminal will be able to accommodate a ship that is 1,300 feet long and be LEED certified. Groundbreaking for the construction of this new terminal has already begun.
For more information check out these two press releases, which are the places I got my information from.
Royal Caribbean's Press Release On Symphony of the Seas: Click Here
Royal Caribbean's Press Release On The New Miami Cruise Terminal: Click Here
Both links will take you away from RyG's Cruise Guide and will open in a new window.