Why is my calling speaker gets low sound?

@mohamedatfaizan start off by cleaning the speaker grill. Those speaker openings are very small and a lot of debris collect in those. If that does not work, you may need to consider replacing the speaker.

iFixit does not yet have a guide for this. Use something like this to replace it.

Replacement speakers are readily available online. Just select a speaker that is for your exact model.

Of course, you can always check the proper components on the motherboard.

While you work on your phone, 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.