I was thinking that this phone has two speakers but it looks like it uses the earpiece speaker as a ringer too. I could be wrong.
Anyway I looked at a Nokia Lumia 635 screen assembly and it turns out you can take out the earpiece speaker from the old screen. You need to pry the eariece speaker off as it's stuck with adhesive on top of the metal plating.
Took one out successfully so it isn't too hard. Sometimes the pre-installed one can be faulty.
I have a question though:
Does your phone have a speaker at the bottom back?