Jacksonville is about 1.4 times bigger than Phoenix.

Phoenix is approximately 1,342 sq km, while Jacksonville (map shows its 197 named neighbourhoods; the area covers the whole city) is approximately 1,935 sq km, making Jacksonville 44% larger than Phoenix.
Tip: This to-scale comparison of Phoenix vs. Jacksonville 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.