I think using imgbb.com is the easiest way to post images from your phone.
Visit the website, upload your image, and select and copy the BBCode full linked embed code from the menu.
You will only need the direct image url including the IMG tags, the URL tags around it can be removed.
For example, this:
Code
[img]https://i.ibb.co/bsCGphF/grafik.png[/img]
becomes this:

Another option would be to unlock the image upload feature by gaining customer perks or donor forum access.
This features lets you browse and upload to d2jsp directly:
https://forums.d2jsp.org/topic.php?t=83903674