If you have an Apple Watch 9BMetrics solves your worries about the iPhone. Just start recording and put it safe in your jacket or backpack. All running information is show in the 9BMetrics Apple Watch Application.
First row shows time and distance that you have been running.
Center space shows speed. Turns orange at 19km/h and red at 20km/h and gives you haptic feedback when crossing these boundaries.
Last line shows battery reserve and estimated remaining distance. Turns orange when reserve is less than 30%.
As you know watch turns black when not used but just lift your arm and it will light and update the data.