Unless you're going to be doing some crazy equalizing then the iPhone will be plenty.
I use the Neo's on my ancient OnePlus 6 and would never go over half it's volume unless it's a really old non remastered song. They really are that easy to drive.
However, a physical volume knob and peace of mind if you ever want to upgrade to harder to drive headphones would be a nice thing to have with a seperate dac amp.
Unless you're going to be doing some crazy equalizing then the iPhone will be plenty.
I use the Neo's on my ancient OnePlus 6 and would never go over half it's volume unless it's a really old non remastered song. They really are that easy to drive.
However, a physical volume knob and peace of mind if you ever want to upgrade to harder to drive headphones would be a nice thing to have with a seperate dac amp.