Most PC motherboards by default only want to put out 100 mA (or 1 tenth of an ampere) on USB. Phones (or other smart things) often use the data lines to communicate with the PC/Laptop/charger, and are saying "Hey, give me more current. I can take it!". They can then output approximately 500 mA. I'm not familiar with your phone, but it sounds like it won't charge until it establishes that there is a higher power available. Hrm, there must be a 12-step program joke, in there somewhere! The USB 3.0 spec calls for as much as 1.8 amps to be requested!
I know that Blackberries will request the higher current. These things with smarts will (usually) try to avoid killing each other. Most USB chargers make their advertised maximum to really mean "as much as, if it can be used, or is requested". I have a 2A wall charger that I routinely use on Darwin all the time. I have used it for a long time on my phone, I notice that it charges up faster.
I think where people get in trouble, is trying to use a simple PT that has no battery. Look at the display on Darwin, we are often drawing in the vicinity of 2 amps. A vehicle cigarette lighter/USB charger? Many of these put out more current. Many/most PVs are just a battery, a switch and a heating element, not much smarts going on there.
If you connect a switch and a heating element to your laptop and try to suck 2 amps out of it, it may try. It may also
let the magic smoke out of your laptop/PC.
I tend to keep wall chargers around for charging all my USB devices. If there is mis-communication, I'd rather blow up a $2 wall charger than any laptop/PC that I own.