Hi,
Try starting the phone in [https://thedroidguy.com/2019/03/boot-samsung-galaxy-j3-safe-mode-recovery-mode-wipe-cache-partition-factory-reset-tutorials-1072105|safe mode] to see if it works OK.
''If it does'' then a downloaded app is the cause of the problem.
You’ll need to uninstall each downloaded app (start with the latest ones installed or updated), one by one and test the phone in “normal mode” between each uninstall. When the phone works correctly then the last app that was uninstalled is the culprit.
''If it still doesn’t work OK'' in safe mode, try resetting the phone, using the phone’s ''factory restore feature'', to check whether it is a hardware or a firmware problem.
Perform a backup of the phone, using the phone’s ''backup feature'', before doing a factory restore.
''Be aware the a factory restore will erase all your data and downloaded apps. It will restore the phone to its’ factory default (or last updated) condition. It will be like when you first bought it. That is why it is '''important to backup the phone first'''.''
Once the backup has been completed, factory restore the phone.
When the factory restore has been completed check if the phone works normally.
''If it still doesn’t'', then you have a hardware problem.
Is the headphone icon on all the time even though the headphones are not installed? If so, I’m just wondering if there is a problem with the headphone socket.
Has the phone been dropped or gotten wet at all?
In any case it will have to be opened and the problem further investigated.
Here’s a link to the ifixit [[Topic:Samsung Galaxy J3]] guide, which may be of some help.
''If it works OK in factory default mode'' , using the backup that you made earlier, restore the phone to what it was using the phone’s ''restore feature''.
When the phone has been restored check that it is still working OK.
If it does, then the reset has resolved the problem