I understand a lot of people struggle to upload to Steemit in general and specifically from smartphone. This finally worked for me after reading a bunch of tips and trying for 3 days.
I'm using an android phone (Huawei P smart). Hopefully this works for all smartphones.
Go to your phones settings and disable sleep.
Find and copy your private posting key (go to steemit account in a webreader, not the eSteem app, and check under wallet tab).
Prepare snap according to step 8 also make sure the video is mp4. Convert if not. Smaller file size is quicker. Big might be difficult. Mine was about 150 mb after converting to mp4.
Use Firefox webreader and log in on D-tube using regular user name and private posting key (DO NOT USE YOUR REGULAR PASSWORD).
After logging in with user name and "PUK" start the video upload by clicking the menu to the left and then the cloud icon that says "upload".
Click in the box and choose your video.
Do not do anything until video is fully uploaded. Don't check Facebook with your phone. Don't switch to any other app. Let it sit. Play ukulele.
When the upload is finished: add snap. If you get a message saying its too big: take a print screen of the picture and trim the edges using the phone editor. Doing this will keep similar quality but significantly reduce file size. Preferably prepare this before upload to avoid hastle. Let it upload fully before going to tags, headline and description.
Put in description, headline and tags. At this point you should be able to swith back and forth between your notes to copy description. However you are able to edit this after publishing so perhaps publish first (or keep info in your head/sidenote) to avoid problem.
Press SUBMIT.
Contact an app developer and ask them to make a D-tube upload app.
Hope this works for ya, it finally did for me!
Here's my video, enjoy:
Peace