Are you connected to phone (or did the build) through the same computer/system? If yes this must be something with font, ISO not supported by phone.
On your tutorial (from the video) you have WAY too much copy! Just a quick critique. Your issue is definitely with the font. Try a different more standard font as a test to see if another would work.
I think it is just my phone. It works on every other device I've tried. Very weird, but I'm just glad its working on other devices. I can see what's on it from the computer. It worked for quite a while on my phone as well.
I've just had the same problem. I found an awesome font that's already on my computer and in Buildbox and works fine, but as soon as I play it on a device I just get black squares
