Since 3.5mm jacks with insertion leaf switches are larger, the audio chips instead check for approx. 32 Ω of impedance on the audio channels, or connection between the first two pins (MIC and GND), which doubles as button press detection (some phones, including every Samsung one, check for several resistance levels, allowing for separate ⏮⏭ buttons rather than just the multipurpose ⏯). This makes sure that (high-impedance) line-in devices whose plugs bridge the first 2 pins get detected (as a side effect, your headset with mic and 1 button will only show up with the micless icon if you hold the button while plugging it in).
Therefore, phones do detect line-level devices vs headphones or aux-in ones (or at least have hardware to do so) but other than perhaps some EQ and level adjuatment in the DAC, there is no effect.
You’re practically right but…
Since 3.5mm jacks with insertion leaf switches are larger, the audio chips instead check for approx. 32 Ω of impedance on the audio channels, or connection between the first two pins (MIC and GND), which doubles as button press detection (some phones, including every Samsung one, check for several resistance levels, allowing for separate ⏮⏭ buttons rather than just the multipurpose ⏯). This makes sure that (high-impedance) line-in devices whose plugs bridge the first 2 pins get detected (as a side effect, your headset with mic and 1 button will only show up with the micless icon if you hold the button while plugging it in).
Therefore, phones do detect line-level devices vs headphones or aux-in ones (or at least have hardware to do so) but other than perhaps some EQ and level adjuatment in the DAC, there is no effect.