METHOD TO HOOK UP PHONE'S AMAZON MUSIC, PANDORA, ETC. TO CIRCA 1978 RECEIVER

Well, thank you all, including ebm for your rule of etiquette. I agree with you on that.
I ended up connecting via just a $4.00 RCA to 3.5 cable into the iPhone and into the tape section of receiver as CD player was already on aux.  The receiver was built before CD players. Works well. Research suggested the signal quality via cable was better than cheap Bluetooth, even though I lose the convenience of having the phone anywhere I want in the room. 

Very important 2 threads and your shouting.Good luck!

Chromecast Audio would work with a cheap rca splitter cable.

+1 on reubent's bluetooth receiver option.  I use this on my office system at work and it's fine.  With bluetooth you can control it from across the room and don't have to mess with cables.  The one I have plugs directly into an AC outlet and has rca cables that go to the aux input on an integrated amp.  I don't see the one I have on Amazon anymore but there are plenty of inexpensive options.

Cheap bluetooth receiver. Connect bluetooth receiver to old receiver through aux input. Connect via bluetooth from phone to BT receiver.....

plug phone into aux or tape, cheap headphone to RCA cable all you need

Yikes, Sorry for the all caps shout.