Aum would be my first choice but I also use Zenbeats and cubasis 3.
Loopy Pro also has a a very powerful mixer and routing capabilities.
I never use GarageBand but I guess it can do the trick too
When you say “as many tracks as possible on one page”, I assume you are saying you want to see all six stereo tracks on your iPhone, which is why you made the distinction versus iPad? To my knowledge, you’re not going to magically get full visibility into six full stereo tracks in a screen as small as the iPhone.
How about iZotope Spire? It’s pretty basic but quick and easy to use. More of a multi track audio sketch pad than a full blown production tool but I like it for capturing ideas.