After export of composition I get colored lines

Hello

I'm new to After Effects, and I've tried to create a simpel composition and export it. But the result is not very good.

First of all, I've shot a video on my IPhone and then I've added to my Mac and after to the composition. So just for simplicity I've directly exported it, BUT the result I get cannot be opened in QuickTime. When I try to send the video to my IPhone it cannot be played there as wel.

So I've read somewhere to use Media Encoder, so I've done using the Media Encoder and the result is just vertical colored line and that is it. (see the attached file)

Anyone has any idea why?  What am I doing wrong? I thought exporting should be simple and it should just work.

So basically I need to compose a video then put back to my iPhone and it should work.