This advice came in from a user in our beta group. Use Good Reader to import GPX to Gaia GPS on your devices:
A great thing about Gaia is the ability to import gpx files into the app. I found an easy way to do this on the iPhone or iPad without having to use a computer.
There’s an app called good reader that allows you to login into a web site and download files (like backpacker.com or every trail) you can then email the gpx files within good reader to email@example.com.
This works great and is pretty easy. No need to use a computer any more.