Did you have this problem after September Update?
I too have this problem.
I ask Nokia support team.
Solution : Reboot by method below！
Press "Power button" + "Volume Up button" at same time for 10 Seconds long. Release them after phone vibrate.
After I try, My phone speaker is finally return！
You might want to try！
And you can clean the headphone jack by "Cotton swab".
I have this problem before.
The headphone jack plug-in sensor is too sensitive by dirt.
After clean it would be fine.