Howdy @thedamus,
I get that error ( “Error: unable to contact server.”) when I do not have an internet connection. Especially, during uploading photos.
Without an internet connection, browsers show steemit, and even show the new post screen. When you upload a photo or submit the post, that is when the server is contacted.
I think you do all things with your phone. After getting my new phone, my internet connection is slower at my job and some other places. It doesn't make sense. I suspect my mobile service provider is slowing down my access. Maybe this occurs for you.