If you are using iCloud to sync your vault, something like this can be done with iOS Shortcuts.
What I do is use a shortcut to type or dictate (separate shortcuts) to append text to an existing file (Quick Notes.md) in my iCloud vault. The shortcut doesn’t open the Obsidian app, it just provides an input box to type or dictate your note.
I like to have all my little snippets collected in a single note, for more convenient processing later. But I imagine you could set up a shortcut to create a new MD file for each entry you create.