Password page doesn't work from phone but does on computer

I create a protected page using the built-in WP feature at https://www.washingtonmuseumassociation for our nonprofit board to access. There is a link in the footer widget to it, “Board Access”. When testing it, it only required a password on my computer one time and now opens every time without additional security; the breadcrumb reads “Home/Protected: Board Access Page”. Maybe the page remembers the IP addresses of those who’ve already logged in? Whatever, this would be fine except I can’t log in to it on a smart phone. I can see the rest of the website just fine, but the board access link just leads me to keep entering the password with no success. I’ve deleted the page and recreated it, but that doesn’t change anything. I’ve searched the web and WP forums and haven’t found this issue listed anywhere else. I am not a programmer, I just update content for our organization.