I used to use my iPhone as my cycling computer. I had the Wahoo Cycling app which would automatically upload my rides to Strava. It did a decent job for me, but I had a few issues. First, I had a few occasions on hotter rides where my iphone shut down due to higher temperatures. Secondly, I was always worried about water or sweat dripping down on my phone. As others have said, if you leave your screen on constantly to monitor speed, cadence and mileage, it drastically ran my battery down. I thought it was lame to even consider carrying a battery charger on longer rides. Lastly, the climbing/elevation data on my iPhone was waaaaay out of wack. It would over exaggerate my climb data and give me false confidence.

I finally bit the bullet and bought a Garmin 810. Obviously not the cheapest option, but it addressed most of the issues that I described above. It automatically sinks up my data to my iPhone and uploads ride data to Strava. On longer solo weekend rides I can send my wife a link where she can track my route in real time. This comes in handy should a problem arise.