I've just thought of one thing you could try if it does turn out that you can't delete your mobile number and leave that field blank, although I've never actually tried it myself to see whether or not it would work, as I was only ever registered as a private seller before I gave up selling on eBay. If you don't want your contact number being displayed on eBay why not just replace the existing phone number with one that doesn't exist? If you do decide to replace it with a random number you've thought of off the top of your head then it may be best to phone it and check that it isn't a live number first! If you dial the number and get an answer just say something like "Apologies, I think I've dialled the wrong number" and hang up. If, however, you get the standard "The number you have dialled has not been recognised. Please check and try again" message that you tend to get if you dial a number that isn't registered then use that number instead.
