The iPod nano (5.4mm) is even thinner than the iPod touch (6.1mm). It still has a headphone jack.
And 5mm is the absolute minimum thickness for a 5-inch device; you really don't want a slab-shaped phone that is any thinner, otherwise the structural stress on it will genuinely make it warp/bend/crack in people's pockets.
And 5mm is the absolute minimum thickness for a 5-inch device; you really don't want a slab-shaped phone that is any thinner, otherwise the structural stress on it will genuinely make it warp/bend/crack in people's pockets.