Phoenix is about 1.4 times smaller than Jacksonville.

Jacksonville (map shows its 197 named neighbourhoods; the area covers the whole city) is approximately 1,935 sq km, while Phoenix is approximately 1,342 sq km, making Phoenix 69.35% the size of Jacksonville.
Tip: This to-scale comparison of Jacksonville vs. Phoenix uses the Mercator projection, which distorts the size of regions near the poles.
Our free app, MapSize by MyLifeElsewhere — compare any two places, to scale on your mobile device.