Below applies to production mode. There is a discussion button at the bottom in the Beta and Experimental modes. But see T93501: On mobile web, discussion link at bottom of subject page links to page which incorrectly says "There are no conversations about this page".
There's no way to get from a user page to a talk page, neither classic nor Flow. My (Hebrew) Wikipedia user talk page is flowified, but I cannot get to it from the user page. I can get to it from Special:UserProfile, but that's far from perfect.
Given that classic talk pages are barely usable on mobile anyway, maybe it's not very important to provide a link to them, but flowified user talk pages should definitely be accessible from the user page and possibly also from MobileFrontend's hamburger menu.