Question Tape recording from phone

Sep 23, 2023
I have a Sony TC-U2 tape deck and Sony STR-212S receiver and I want to use both of them to record from my phone.
I have a newer cheap stereo that supports aux and bluetooth that has a RCA line out.
When connecting the newer stereo to the receiver it amplifies the sound and can play it through the speakers but isn't outputting it to the record out on the "tape" function.
When connecting the same stereo to the phono input and changing to the phono function it is outputting through the record out.
What am I doing wrong? Both the deck and the receiver in great condition