Recommended Bluetooth Receiver for Speakers?
Yes, indeed there are a few bluetooth receivers out there you can buy.

Altough I don't own one, products made by Logitech never disappointed me. So I'd recommend the Logitech Wireless Speaker Adapter for Bluetooth Audio Devices. It also got good customer reviews on amazon.com. 

 

It features the needed 3,5mm Headphone jack and supports many bluetooth devices(including Android phones and iPhones).

But please do your own research before asking these questions and check out this guide. Stackexchange is not the platform for shopping questions. Also see this site for further information.

Sites that I find useful before purchasing hardware are The Wirecutter and the subreddit /r/BuyItForLife. The last one especially is the place to go for such types of questions.