How much current can an Android phone's USB port supply?
"how much current does a phone USB port deliver?" 


It only delivers anything when in USB-OTG mode. This isn't as well-known as normal USB. This article describes USB-OTG power in more detail.


  The OTG spec calls for at least 8mA and allows negotiation for higher currents if the peripheral needs more power. OTG devices can provide up to 500mA, but in realistic terms, handheld portable electronics don't have 500mA to spare for external loads. 100mA is a commonly accepted realistic maximum.