check the Resolution you have selected on the phone. If it is too low they will be rejected by the eBay servers. If you set the resolution to maximum the server will compress the image to the right size.
If you are using the app perhaps switch to your browser and try that way. If you are using a browser (like Safari) try clearing it's cookies and cache and restarting the phone....it might be a cookie conflict.
Using your browser, you can also view the site in the same view as your PC/Mac by clicking CLASSIC view or FULL on the bottom menu ... this can be a lot easier for some people to upload and navigate than the app or mobile view. It sometimes switches back to mobile view and you need to repeat clicking on Classic.
