Why is my phone speaker is not working

@mohdtannu it could be a stuck headphone jack. Plug your headphones in and if you have sound, then insert and reinsert the jack a couple of times in rapid succession. The headphone jack may be stuck and this cuts the speaker off. Check for any kind of debris inside the headphone jack and use a small non-ferrous instrument to clean it if you have too. Small means small; less that 3mm. For a settings issue, check something like this video and to work on it use this one this phone is still a bit off brand so you will have to use the video and your troubleshooting skills to work on it.

While you work on your drive, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.