I had the same issue Lee - i got fed up of going onto my Mac to resize the pics taken on my phone in an image editor so found easiest way was to upload them first onto a photo library on madaboutkitcars forum (you can set up an album under community -> pictures and album) then click each picture from the album and do ‘save image as’. It seems the image size is reduced by uploading.
I then added the saved images to imgbb and use the full image bb code for my posts
You might not need to do this now Wozzy - when I uploaded using Safari on iOS 13 at the weekend it gave me the option in IMGBB to select the image size at point of upload direct from the photo stream.