How to read card reader on iPhone
Trying to see photos from trail cam reader card
iPhone 7, iOS 15
A friendly tip: have a bit of patience when you ask a question. This isn't live chat and Apple Support does not participate in these forums. We're all just fellow users here, helping as we have time and knowledge to share, so it may take more than the very short time you waited before anyone even sees your question, much less has time to formulate a diagnosis and post a suggestion.
As to your question, presuming that this is an SD card reader that you're trying to use, see:
Connect external storage devices to iPhone - Apple Support
Regards.