Answer
Go to the following website and choose the device you wish to look at:
While looking at the phone specifications click on the gray bar titled, “TO SEE THE FULL SPECIFICATIONS WITH IN DEPTH DETAILS CLICK HERE”
Scroll down to the connectivity section and look for Bluetooth. Please note that the details at this site may not be completely accurate but are a good starting point.
An alternative method is to search the listings on the Bluetooth SIG website:
https://www.bluetooth.org/tpg/listings.cfm
However, you may need to know the manufacturers part number rather than the popular name. For example to find the Samsung Tab 4 you should search for SM-T230, this part number can sometime be found in the Phonearena site mentioned above.
Another method is to visit the XDA Developer Forums and search/ask in the forum for the product your are interested in: