Birmingham is about 3.5 times smaller than Phoenix.

Phoenix is approximately 1,342 sq km, while Birmingham (map shows its 87 named neighbourhoods; the area covers the whole city) is approximately 381 sq km, making Birmingham 28.38% the size of Phoenix.
Tip: This to-scale comparison of Phoenix vs. Birmingham 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.