Whilst it's an imperfect system, someone clearly had the same problem and has made a very simple toolkit for enabling the bbcode to be obtained from photos using the Flickr app.
In short, a summary below:
- Open image in the Flickr App
- click the arrow to denote the "share feature"
- tap "copy URL"
- open https://tools.sportscard.trade/ on your mobile internet browser
- press "Menu"
- press "Flickr"
- paste the URL you copied from the Flickr app
- BBCode is generated
- copy the BBCode and paste it to the forum as you would when creating any normal image post/thread
I know some other methods are available, and as I say, this isn't perfect, it's pretty simple & easy for what it is. I know I've been searching for a way to do it for some time now, so this is pretty helpful to me. Hopefully this is of some value to others, too.