I Can't use gajin store with a Steam account?

In this last “Tokushu Heiki” event I gathered materials to create the missile, but soon after I finished, I would like to sell the leftover items. But when entering the store I realized that it was necessary to verify the phone number, when I click on that it takes me to a security tab where I can’t do anything because I’m logged in with Steam. Can I make something to sell on the market?

Try going direct to the website in a browser and selling stuff there.