You can reply to any Thread or post that is still open by choosing reply or quick reply at the bottom right of the post you wish to repky to, as for quoting, because you didn't add any body to your Thread I can't quote you, but once you have chosen the post you wish to reply to, after the new text box opens up there will be a quote tab to the top right of that new box.
Please bear in mind that some posts & Threads you will not be able to repond to because the post is locked or is archived.
If you're using the mobile site, you can only do simple posts. No replies, no quotes.
Most browsers on mobile devices have the option to use the full site, why not do it that way? it's what I do when I am on my tablet.