You can import the GPX route using the web app but the currently available IOS MyRoute-App does not provide any navigation instructions. It can record where you've been, and you can plan a route and see all the routes that you have created in MyRouteApp-Web.
They are developing MyRouteApp mobile which is a separate App and supposed to be available 18-2-2018. Any route that you have in your route library will apparently sync to this so you can then navigate.
No idea whether it's any good yet!
One thing to note if using iphone for navigation is that it's CPU intensive and the phone can get warm. If it's in a waterproof case on a hot day it may well get hot enough to shut down to protect itself. Also, you will need power to the phone if riding for any length of time :)