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I can't make sense of this statement in the article - it seems to be off by two orders of magnitude.

A typical smartphone battery (Xiaomi Mi4i) is specified at 3.12Ah @ 4.4V. Multiplying, we get an energy content of about 50 kilojoules, which is about 1/200th of the a typical daily human energy requirement (10MJ).

As snaily said above, your smartphone really doesn't need 2500kcal/day. I think what they were trying to say is that, given 100% perfect energy transfer, you'll be able to power your phone from your daily calories without missing much. As in, "this is so much, you can power a phone without realising something's missing".

Dietary calories are actually kilocalories. 2500 kcal is approximately 3kWh..enough to run a thousand phones for an hour.

What's impressive isn't the efficiency of the body's use of energy (electric motors are already pretty good) , but rather how efficiently it extracts and stores it.

If smartphones had our stomachs, we wouldn't need to charge them..just let throw a hamburger in there once a month.