Can this be done on an iPad or iPhone? If so, I must be really stupid because I cannot figure out how.
You should definitely be able to, I think by dragging/highlighting the text you want to quote. Almost like you’d do to copy and paste something.
A “quote reply” message should come up by the text. Click that and it should open a new reply message featuring the quoted text.
Feel free to play around with some test posts in this thread.
Nope. Doesn’t come up on my iPhone. I’ll try my iPad later. Thanks.
Works on my iphone. Hold your finger down until the selection pops up for copy paste, the select the area and the ‘quote’ icon appears. 
The quote icon never appears for me. I can select the area but then just have the option to copy, define or share. Ahh well.
I’m using an android device but I find that the quote button/hover thingo occasionally doesn’t appear if the copy/select buttons/hover thingos appear.
Not sure how to control this.