Hmmm OK, I think you need to "stop, plugging stuff into stuff ... before you blow something up!
I was seriously confused as to what it is you were trying to do??? Near as I can tell ... it seems you "think" that unit has an amplifier built in that could drive "outboard speakers??"
Near as I can tell, it does not?? If it did ... there would be "Speaker Jacks" on the back of the unit for "external speakers??" It does not have those?? It's a self contained unit the built in speakers can, play an LP or apparently you can use Bluetooth and play "stuff" from your phone on it. It's a "self contained unit" it's not meant to "drive outboard speakers." The video on the link pretty much outlines what it does. It's kinda cool actually.
The RCA Jacks, that I think you are trying to use to drive, speakers??? That is "NOT" what they are meant to do! Your missing "gear" if you want to uh complicate things up as it were. You need a "Receiver" (Tuner, Preamp and Amplifier) all one chassis, or an Integrated amp (Preamp and Power Amp no Tuner) or a Power amp with volume controls.
The "speakers" get hooked up ... to the piece, you don't have and the Crosley using the rca jacks, on the back of it, gets plugged into that piece of gear you don't have.
Have a look here ... you can't get simpler than adding this unit. :
https://www.ebay.com/itm/KINTER-Min...rentrq:aef340e21660ad4b4799f77bffffc785|iid:1
I don't have one, of those but it looks cool. Now assuming that unit does not "need' a "Phone Input??" It would get plugged in where they showing the "MP3" player. And the speakers go where it shows the speakers, on the speaker jacks.
If it needs a "phono Input??" Then a baby receiver/ with a phono input or powered speakers would be the answer. It should say if any input is fine or if it "needs" a phono input somewhere in the documentation uh maybe???
I don't think it needs a phono input but I don't know. At any rate, since it has "Bluetooth" and it is a TT. It is/would be your source for sounds. And most likely if it gets plugged into the "approater hardware" the built in speakers would be "bypassed??"
Hope this sorta clear as I was stumped at first.
And if you wanted to venture into a uh modest "Vintage, Integrated Amp ... LOL, the cost of entry can be low ... :
https://www.ebay.com/itm/RadioShack...e:g:rgIAAOSwSrxbNmDY:rk:5:pf:1&frcectupt=true
I have a couple of those units ... I bought new! And they still work just fine and they do have a phono input if needed.