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 other factors besides its BT usage for streaming? Unless you are looking at using the mobile phone exclusively for music streaming purpose. In that case, why not explore much cheaper Android based DAPs which are focused on music play, like FiiO or HiBy? Thereby you can also use it as a portable music player.