Exceeds safe limit for microwave exposure
Focusing a few watts of microwave power onto something about 5cm on a side results in a power density several times the accepted 0.01 watt per square centimeter safe limit for human exposure.
Geoffery Landis at NASA came up with this idea over a decade ago, and it's patented under US patent #6,967,462. The Ossia patent is just a few tweaks on the Landis patent. The safety issue was described in the Landis patent. That patent proposes detecting backscatter when the beam hit something other than a properly tuned antenna (such as a human) and reducing the power until the human gets out of the way. That might work, but it's iffy from a safety perspective.
At laptop scale, this might work, because the target area is bigger and the energy density of the beam can be reduced by using a wider beam. But charging phones while people are wearing them? Bad idea.
There's no problem doing this. Microwave power transmission has been demonstrated many times. It's just that you don't want people in the beam.