Phones are not great as a navigational tool due to the unreliable nature of GPS signal being picked up on your its tiny antenna, poor battery life, bad weather resistance and durability compared to dedicated GPS units after a large number of smart-phone related rescues that had to be carried out. If you want to be modern and use super accurate GPS (in the form of an app or a dedicated device) then good on you but be sure to take a map and compass with you (aswell as confidence on how to use them). Remember: if you get lost retrace your steps. Then, if you still can't find the path to your goal, retrace your route all the way back down to the start of the walk and try again another day: after taking another look at your map at home (else you will just get lost again).
By the way even the Iphone 5 isn't gonna be as good as a dedicated GPS device for navigation (although it will be kinda epic - probably).