I am on the Apple ecosystem, but for your requirement I won’t suggest iPhone. Your DAC has aptX and LDAC codecs, neither of which Apple gadgets have. So you’d be only transmitting SBC or at best AAC. Get an Android phone with aptX HD or better still, LDAC codec support.
But a more basic question. Shouldn’t the choice of a mobile phone depend on many factors beyond just Bluetooth streaming? If your main focus is music, you could explore affordable options like Android-based DAPs or even a
SafeLink Wireless phone, which can serve as a dedicated portable music player while still providing essential smartphone features.