Is your phone on a contract or a top up card.

If you are on a contract it sounds like a technical issue.

I assume by your feedback you are already an ebay member, but have you sold via your phone before ?

If not then perhaps you need to have the phone number verified before you can list via it.

Personally I don't see how anyone could list through a phone  I won't even own a mobile let alone try to figure out how to list on ebay through one [had enough of them when I owned a business in sydney],.

If you can't figure it out you will have to go to LIVE HELP  tomorrow, they're closed now, & ask them what the issue is if the phone is registered as an ebay members phone for listing.

good luck