The phone will do what you want, some folks find that RideWithGPS works very well. Battery life may not be as good on a phone as with a dedicated cycling GPS unit, kind of phone dependent. As well, you may be needing a constant data connection to use the phone, while a GPS unit has the maps and course loaded on the device. There are work around a for this, as BTW and I'm uncertain as to this.

Others find the phone screen is hard to read in direct sunlight, but the larger phone screen may be easier to read. Then there's the argument about do you want your $600 phone on the h-bar, as opposed to a $250 GPS unit, and this begs the question do you rely on the phone for a lot of other things that would screw you up if the phone got wet. Yes you can get a Lifeproof or Otterbox case, but would you use that daily ?. Garmin GPS units are typically waterproof as BTW. The Garmin units that use a touch screen - so 810,820 & 1000 work well with full fingered gloves, so work in colder weather, where as a phone screen requires taking a glove off or using special gloves.

One neat trick I leaned today is from this post.

http://www.bikeforums.net/road-cycli...awesome-3.html

Seems the Garmin watch, not sure what model, can accept a downloaded course and will buzz, etc.. before turns. The post indicated the use of a dedicated Garmin 800 unit as well to show the course on a map.

I've been very happy with a Garmin 810 for turn-by-turn directions on courses I pre created in Garmin Connect. It's been very reliable for me, though TBT sometimes lags in complicated intersections with fast turns in close proximity. Not sure any other device is any better. An $810 runs about $250 these days. Others have found the 810 flaky, maybe the 820 is better, but first generation Garmin devices usually have issues, just heads up. I've 4 mos. on an 810 and 50+ rides with no issue, so maybe the software is now stable.

I'm also using my 810 as the only bike computer on multiple bikes, so the investment will pay off as I no longer need to buy replacement Cateyes when they fail. As well I already have and carry a phone anyway, so it's not an issue. With the Garmin 81o/820/1000 as well as the Wahoo units, you can create the course on a computer, save, then easily download off the Garmin phone app to the bike GPS unit via the BT connection. It's very easy. After a ride, you stop the course and ride and press save and it uploads to Connect, RWGPS and Strava automatically. I'm in love with this ride recording system.