make sure you join the clyde group on Strava - it's good for motivation.
http://app.strava.com/clubs/clydesda...bikeforums-net
Also, I'd recommend sticking your phone in a ziploc bag and putting it in your jersey pocket. I don't know that I'd want my expensive phone on some fragile little mount on the handlebars, exposed to the elements & at risk of flying off if I hit a bump. If you don't have or like bike jerseys, then maybe a bento box for your top tube would be a good place. I have a Note 2 and it doesn't fit in anything, so I go jersey pocket.
This is the top tube carrier I got -
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
I only use it when I bring a little point and shoot on rides and as I mentioned, my phone won't fit in that top sleeve. I don't know that an S3 would either but it would fit inside for sure.
Good luck and welcome!