Any 5 volt charger with enough amperage capacity for your phone will charge your phone at the exact same rate. It will not harm your phone battery, nor your Kindle charger, but your phone will neither charge more nor faster. The extra amp capacity of the Kindle charger will not be used, as the phone's charging circuitry controls that. What would damage your phone would be charging it via a higher voltage charger, higher than 5 volts. Don't do that to the Kindle either, of course...
I do this all the time with my Droid 3. No problems. Charging with a too small amperage capacity takes longer, but that's all. Any 5 volt charger capable of enough amperage is identical in effect.