Phones take pix with giant file size now. Apple now defaults to a .heic file type which causes problems. Its all a plot to make you buy "CLOUD" storage.
You have to reduce the size and or change file type to jpeg.
I have not found a direct way on my iPhone to reduce the file size other than cropping the photo which isn't always desired.
I Air Drop to PHOTOS on my MAC and then Export to the Pictures folder as a jpeg with a "Large" file size
or
I use imgur.com to store pix I want to share and then paste BBcode