How do I get turn-by-turn instructions on Android?

I was browsing for cycle routes in Birmingham when I found this web site.

It’s great that I have got a suggested route of 26 miles. I would like to use the GPX file to give me voice directions in Google Maps on my Android phone but I haven’t worked out how to do this.

I’ve now got the round trip route set up in Google Maps on my phone but the Directions button isn’t present or doesn’t work.  What's a simple way to get the suggested route as a turn-by-turn voiceover on an android phone?