On iPhone, Garageband is the DAW peeps usually start with. Exporting MIDI from it to anything other than Logic can be a pain but there are workarounds.
A direction that appeals to me personally is using a master sequencer app, so that the music is created and arranged mostly as MIDI.
AUM by itself is just a mixer with some useful utilities. It has no timeline as others have mentioned. It also lacks a step sequencer or any other built-in sequencer. There are a lot of new IOS users these days who ask questions about the “AUM sequencer” and they seem to struggle when others try to explain to them that it is about as real as the Easter Bunny and Santa Claus.
So anyway, the workflow I’ve been exploring is using a master sequencing app for creating and arranging a song as MIDI. I use AUM to try out ideas, especially with generative apps like Piano Motifs, Rozeta Suite, etc. AUM is where I have the master sequencer play out the song, and have audio generated from that.
Then I export any audio recorded in AUM to Zenbeats. Zenbeats has the easiest workflow for taking importing audio files from other apps and arranging them along a timeline. Garageband has the 2nd easiest - it’s 2nd place because it takes one more step than Zenbeats.
I’ve experimented with the following apps as candidates for master sequencer: Xequence 2, Nanostudio 2, Sunvox. What they all have in common is linear sequencing capability, or at least the option to sequence linear style. Drambo would probably be better suited for someone who prefers pattern style and is willing to practice triggering the right patterns at the right time while recording a song.