We are installing porcelain tile in a galley kitchen approx 5x12 ft. Should we use 13x13 or 19x19 tile? Was told that larger tile will make kitchen appear larger? My gut feeling is to use 13x13, but maybe I need to step outside my comfort zone?
It is purely personal preference. Big tiles work fine in smaller spaces.
Another consideration is how that spacing ends up on the edges for each tiles size. With the 19" tiles, you'll have 3 whole tiles and 1 1/2" slivers on each side (assuming exactly 5ft width). That may look fine or may look odd depending on any overhangs on your cabinets.
With 13" tiles, you will have 2 whole tiles and 2 almost whole tiles.
The size of the kitchen should dictate the size tile you use for the space. Smaller kitchens will look more uniform with smaller tiles for wall accents or the oven backsplash. A kitchen with more space looks especially classy and modern with large tiles on the walls and backsplash areas.