Since you're still new and have 0 seller feedbacks Listia won't actually let you do a GIN. You need to have your sellers wings before you can start adding gins to your auctions. Sellers wings are earned after you complete like 5 or 10 successful auctions. And you also may want to verify your account as well so you can get that trusted seller badge :)
From a computer on the lower left hand side of the page page where you can see your open listings, watch list, what's trending etc, there's a link that says verify account. That's where you do the verification. There's a few steps. Like linking a PayPal/credit card (they won't charge a single cent for entering your card number and I've never been charged anything in over 2 years on here. It's more so just to prove you are who you say you are), linking your phone number, FB, twitter etc. And if you do them all you get the special fully verified level 1 badge. Being verified let's people know that you more than likely are not a scammer and it definality let's people know you don't have more than 1 account on here. If you notice around on lots of kinda expensive items people list with low feedback scores most people will always ask please get verified since if you are you're likely to get more bids and higher bids. It takes about 5 mins to complete all the steps but it's well worth it in the end because of how much more you can make on Listia :)
With the phone though, and this is the mistake I made, you only get 3 chances for Listia to call you. After that you can never verify your phone again. I was having bad connection problems when I tried and I used up my 3 which now keeps me from getting level 1. I've done all other levels of verification though. So be sure when you do your phone you have good service so you don't miss the call or have it go to voicemail or anything like that. I've been trying to get Listia to give my phone one more chance but after 3 tries, nope that's it.