Yes, you can control the volume from the phone using the phone's volume buttons just like we do in case of any other headphones.
Apart from the design difference - the biggest difference is AirPods are wireless while EarPods are not wireless. The AirPods comes with lot more openings compared to EarPods.
If you have already paired your AirPords with your iPhone and want to pair with any other iPhone, you need to follow the below steps.
Step 1: Open your AirPods charging case
Step 2: Tap "Connect"
Step 3: Press and hold the "pairing" button on the back of the case.
Yes, you can connect Airpods with iPhone 6.
Look past their offbeat design and you'll find that Apple AirPods' compact size and high convenience factor are a winning combination.