You can also try to enter settings on your iPhone, click Bluetooth, hit the "i" next to your Powerbeats 3. Forget the Device. Allow it to re-pair with the iPhone and make sure nothing else is on that it is also paired with. I have been quite a distance from my iPhone and kept a connection so I'm guessing it is not distance.
I sweat daily in mine and haven't had an issue but there are threads on the Apple Store that folks do believe sweat / moisture caused problems.
If resyncing the device doesn't work, your best bet is to open a repair ticket with Beats:
https://www.beatsbydre.com/support/service-warranty
You are still within your one year warranty.