Old phones as streaming sources

@ghdprentice "The moral of the story is that everything matters."

Yes, I do agree. Maybe some things more than others.

I still have to buy a streamer to find out if it would offer a better audible sound quality to me compared to my actual setup. Due to budget constraints, this is not going to happen very soon.

OP, debating whether the iPhone is a decent streamer with audiophiles who own expensive streamers in the thousands or even tens of thousands may not be worthwhile. Individuals should experiment if they are interested. People tend to defend the significant expense they have already incurred, and it's unlikely that they will admit the potential diminished return value proposition that a seemingly free streamer like the iPhone may offer.  Iphone as a streamer amazes me in the following aspects:

1. It is a bit-perfect ready streaming device up to 24 bit 192 khz as long as supported by the app.
2. It is a low jitter performer like other quality streamers;
3. You could run almost all music streaming service provider app on iphone including Roon Remote.  Some streamers like ifi Zen Stream can not allow one to run Qobuz directly and need to go through Upnp app like Mconnect.
4. The iPhone boasts multiple (4-6) GB of RAM, with models like the iPhone 13 having 3.55 GB of usable RAM. It's quick on indexing music files and processing essential features like gapless playback, making it comparable or even superior to some expensive streamers. For comparison, devices like Ifi ZS have 1 GB, Auralic started with 1 GB and recently increased to 4 GB, Hifi Rose has 4 GB, Lumin ranges from 2-8 GB, Aurender has 8 GB, etc. Notably, the Wiim mini has only 128 MB of RAM (Wiim Pro has 512 MB) to support bit-perfect streaming up to 24-bit 192 kHz. 
5. Iphone allows one to play music from local USB storage through external USB hub and adapters.
6. Finally, iphone has the most compact form factor as a streamer.

Apple has already integrated and established these specifications in the iPhone quite some time ago to support online music streaming and local music playing, predating the availability of both cheap and expensive streamers in the market today. One might raise the question, 'So what? How about the most important aspect - sound quality?' To that end, I have personally tried and attested, as have several others. I'll leave it to you to explore if you are interested.

@lanx0003  What you fail to recognize is that noise is the mortal enemy of good streaming, and an iPhone is about the noisiest source possible for streaming.  Streamers go to great lengths to minimize noise while the iPhone does nothing in that regard and has tons of electronics — as well as being a phone — running as it’s streaming music.  No bueno.  I started streaming with an iPhone and it’s fine but it’s absolute crap relative to a decent streamer.  It’s a Jack of all trades and master of nothing, especially when it comes to audio.

posted this earlier, but in case you missed it.  noise is easy to measure.  so while different streamers can be noisier and have higher levels of jitter, some, but not all, DACs can level the playing field, making it unnecessary to spend big $ on streamers.