On an android mobile there are 3 symbols on the bottom right hand side of a message you wish to reply to. The middle one is reply with quote. The same is true of iPhones. There are some restrictions on the appearance of the mobile site, but the reply with quote isnt one of them.
Unless of course you have an incredibly basic cheap phone without a web browsing facility, when you will have problems!!
Always happy to help juniors with basic tech issues. Any other problems please ask and will try to help you.