> The new iPhone pro has a fairly decent 3x (71mm equivalent)

For birds (depends on the kind of bird) you're looking at the 300-800 mm supertele range.

The 450mm equivalent of the long end of my 70-300 is just barely enough if the bird is nearby. 71mm is wider than the wide end (35mm equivalent) and far too wide for anything that'll run/fly away if I get close enough.