Sorry if I am late, but it seems that no one has answered, so I will answer your question. I hope it helps and you manage to resolve the issue, able to attach images to your posts to make them more engaging.

Anyone else?

Funny thing because I had the same problem! However, this was not on a mobile phone, but on a desktop computer.

It seems to me that if you attach images via the "Upload Images" option it does not work, which is your issue. I do not know why, but that is the case for me and what looks like for you as well.

I managed to resolve this issue by selecting the other option "Image Link" and everything seems to be now working fine when I do so. Just upload the images you want on a uploading website, such as https://pasteboard.co/ (self-explanatroy on this website, if you cannot manage to do it, send me a response and I will reply as soon as possible!), then copy the link of the image and insert it in the "Image Link" option.