I used to stream from my iPhone, but using a separate streamer sounds much better, but I don’t think too many streamers work with Amazon HD. I’d suggest eventually stepping up to using a streamer and switching to Qobuz that reportedly sounds better than Amazon HD. But, if you’re gonna go from your phone I’d highly suggest ditching the Apple Camera Adapter and get this LavriCables adapter as it only costs $85 and sounds much better.
https://www.lavricables.com/cables/reference-silver-lightning-interconnect-cable-for-oppo-ha-2-centrance-mini-m8/
You might also consider their dual USB cable that uses separate signal and data legs for better sound and that is usually reserved for much pricier cables.
https://www.lavricables.com/cables/ultimate-silver-dual-usb-a-b-interconnect-cable/
I have both of these and other LavriCables and they’re great. Hope this helps, and best of luck.